My God, what a fascinating question! I'd have to say that Nixon is our most likely candidate, though I'm not sure suicide was in his nature.
So, say he shoots himself. The first problems are that a whole lot of people will hear the shot, and that it will be clear to any emergency personnel at the scene that the President is bleeding from a great, murdering head wound. The coroner's inquest into the death will still be required, President or not, and, just like the examination of JFK's body, will be totally impossible to keep from the press. Especially given the scandal engulfing the White House at the time, the inquest will be handled in the biggest fishbowl in the world.
There's no way the coroner can call it a heart attack. He will have three solutions: Nixon shot himself, somebody else shot him, or he died accidentally while "cleaning his gun". The fact that the bullet which killed Nixon came from the gun found at the scene, and that there was no one else in the Oval Office at the time, nor any signs of forced entry will rule out foul play. And, I think we can expect even a fairly irresponsible coroner to avoid making up a fictional murder of a President, no matter what the political pressure. The choice will really come down to: accident or suicide?
Here is where the political pressure plays a role. Absolutely everyone will want to avoid a verdict of suicide. The Republicans would not want the "taint". The family would not want to hear that answer, and would probably dispute very publically if it was the verdict. The Democrats don't want it either, because they don't want a Nixon legend to grow, nor the onus of possibly having "driven him to it". Even the coroner doesn't really want it; coroners are notoriously reluctant to find suicide as a cause of death, which is why there are so many people killed in mysterious one-car accidents every year.
Based on this, the coroner will bend the laws of physics as far as he has to, and will find the death accidental. Everyone will breathe a sigh of relief, and the American people will buy it, because they want to. They, too, don't want to face the kinds of emotions the suicide of a President would invoke. All in all, much easier to believe he just died in a firearm accident, and avoided prosecution and impeachement by a quirk of fate.
Conspiracy theorists won't buy this, of course. They will come in three varieties: Republican theorists who think vengeful Democrats (or hippies, or commies) did it, Democrat theorists who think Republicans did it to spare an impeachment, and people who think it was a suicide. The suicide theorists will likely be the smallest group. Although suicide fits the evidence better than any other cause of death, it just isn't as dramatic or politically useful as a murder conspiracy.
Watergate will fizzle out, much as it did due to Nixon's resignation, but more completely. Ford, however, will not have the onus of having pardoned Nixon. Nor will the Republicans be seen as negatively as in OTL. Indeed, a certain vague sense of guilt over the whole thing may grip a lot of people. All of this will probably give the election of '76 to Ford rather than Carter.
Ford will face the crises of the late '70s. Whether he will do better than Carter in OTL is anyone's guess. My guess is that he will do a bit better, but it won't save his Presidency. The precedent set by LBJ will mean that Ford will be eligible to run in 1980. He will, and a Democrat will beat him, most likely Ted Kennedy.
Kennedy in the '80s will be a very different President than Reagan. He will not deregulate a lot of industries, benefiting the consumers, but hurting those industries and slowing technological innovation. There will not be the boom for the upper and upper-middle classes that happened in the '80s. On the other hand, the poor, working, and lower-middle classes will be better off than they were OTL. With the strong backing of the White House, unions will do better than they did. Likewise, there will be fewer big plant closings than there were in OTL. Most likely, the first few will happen, and then Kennedy will do something to make later ones harder and more expensive to automakers and other large companies. This will prevent a lot of them. And that will keep a lot of working class Americans in a MUCH better position than in OTL. OTOH, the companies involved will be badly hurt by this, and will stay uncompetitive, which will eventually lead to rancor with Japan, Germany, and other countries. This rancor will be minor in the long-term, but still could present the risk of trade wars, if not handled well.
Other economic trends: the oil glut of the '80s, the beginning of Boomer investment in stocks and retirement funds, and so on, will lead inflation to decline, just as under Reagan. As interest rates return to lower, though historically still very high, levels, and prices stabilize, Kennedy will get much of the same credit of "restoring prosperity" that Reagan got. This will get him victory in the 1984 elections, in all likelihood beating the aforementioned Ronald Reagan.
Kennedy will still boost defense, but not as much as Reagan. He will probably be reluctant to arm the Afghan mujihaddin, though they will still get a fair amount of support. The Russians will be less worried - economically, or militarily - than in OTL. This will mean that Romanov will probably be selected to replace Chernyenko, instead of Gorbachev. Romanov, despite his name, was a fairly hard-line Communist. Circumstances will still force him to reform, but very slowly, and in ways that have little impact. Relations with the West will improve, however, because the USSR will be just too exhausted and troubled to be able to compete, and will need good relations with America. This desire for good relations will be shared by the Kennedy Administration,and so negotiations will go well, and superpower tensions greatly decline.
1988 will be the year of a moderate Republican, probably Papa Bush. His Presidency will be a lot like a continuation of Kennedy's, though there will be a certain amount of deregulation and increased military spending. However, in OTL, Bush only embraced Reaganomics after becoming Vice President. Here, he stays closer to the center, and so his policies mostly just balance out those of Kennedy. The rather boring conditions of modest prosperity for all will continue. Saddam Hussein will still have fought the Iran-Iraq War, and will still need a good way to pay his war-debts. So, chances are, he still goes into Kuwait in 1990. The US will secretly consult with the Russians before acting, and will receive an assurance that they can indeed act on the matter, provided they don't go all the way to Baghdad. As a result, the Gulf War will happen. A less built-up U.S. military will mean more American casualties, but the "maneuverists" will still have done their work, based on avoiding anything like Vietnam, and so the war will still be an American walkover, and will end almost identically to OTL.
President Bush will not face either the 1990-1992 recession, nor the boom of the '90s we had in OTL. A more stable economy, plus a victorious war, will win him re-election in 1992.
The winter of 1992-93 will be a turning point in the USSR. The economic situation there will have become so bad that demonstrations will grow, demanding economic reforms. Romanov wil try to suppress these demonstrations, which will then trigger riots on a very large scale. The Red Army will be called out to suppress the riots. The generals, however, will be shocked to hear that soldiers are deserting and joining the rioters. This will decide them on a radical course of action. The generals depose Romanov, and replace him with.......Gorbachev. And so Russia will begin moving down the same path as in OTL, eight years later.
A democrat, probably not Bill Clinton, will win the elections of 1996, and probably 2000. And, in 1998, a retired Los Angeles police detective named Mark Fuhrmann will publish a book going into the death of Nixon in detail, and at last proving that it was indeed a suicide, and neither homicide nor accident. This book will be denounced by conspiracy theorists, embraced by many, especially in law enforcement, and ignored by most Americans.
So, say he shoots himself. The first problems are that a whole lot of people will hear the shot, and that it will be clear to any emergency personnel at the scene that the President is bleeding from a great, murdering head wound. The coroner's inquest into the death will still be required, President or not, and, just like the examination of JFK's body, will be totally impossible to keep from the press. Especially given the scandal engulfing the White House at the time, the inquest will be handled in the biggest fishbowl in the world.
There's no way the coroner can call it a heart attack. He will have three solutions: Nixon shot himself, somebody else shot him, or he died accidentally while "cleaning his gun". The fact that the bullet which killed Nixon came from the gun found at the scene, and that there was no one else in the Oval Office at the time, nor any signs of forced entry will rule out foul play. And, I think we can expect even a fairly irresponsible coroner to avoid making up a fictional murder of a President, no matter what the political pressure. The choice will really come down to: accident or suicide?
Here is where the political pressure plays a role. Absolutely everyone will want to avoid a verdict of suicide. The Republicans would not want the "taint". The family would not want to hear that answer, and would probably dispute very publically if it was the verdict. The Democrats don't want it either, because they don't want a Nixon legend to grow, nor the onus of possibly having "driven him to it". Even the coroner doesn't really want it; coroners are notoriously reluctant to find suicide as a cause of death, which is why there are so many people killed in mysterious one-car accidents every year.
Based on this, the coroner will bend the laws of physics as far as he has to, and will find the death accidental. Everyone will breathe a sigh of relief, and the American people will buy it, because they want to. They, too, don't want to face the kinds of emotions the suicide of a President would invoke. All in all, much easier to believe he just died in a firearm accident, and avoided prosecution and impeachement by a quirk of fate.
Conspiracy theorists won't buy this, of course. They will come in three varieties: Republican theorists who think vengeful Democrats (or hippies, or commies) did it, Democrat theorists who think Republicans did it to spare an impeachment, and people who think it was a suicide. The suicide theorists will likely be the smallest group. Although suicide fits the evidence better than any other cause of death, it just isn't as dramatic or politically useful as a murder conspiracy.
Watergate will fizzle out, much as it did due to Nixon's resignation, but more completely. Ford, however, will not have the onus of having pardoned Nixon. Nor will the Republicans be seen as negatively as in OTL. Indeed, a certain vague sense of guilt over the whole thing may grip a lot of people. All of this will probably give the election of '76 to Ford rather than Carter.
Ford will face the crises of the late '70s. Whether he will do better than Carter in OTL is anyone's guess. My guess is that he will do a bit better, but it won't save his Presidency. The precedent set by LBJ will mean that Ford will be eligible to run in 1980. He will, and a Democrat will beat him, most likely Ted Kennedy.
Kennedy in the '80s will be a very different President than Reagan. He will not deregulate a lot of industries, benefiting the consumers, but hurting those industries and slowing technological innovation. There will not be the boom for the upper and upper-middle classes that happened in the '80s. On the other hand, the poor, working, and lower-middle classes will be better off than they were OTL. With the strong backing of the White House, unions will do better than they did. Likewise, there will be fewer big plant closings than there were in OTL. Most likely, the first few will happen, and then Kennedy will do something to make later ones harder and more expensive to automakers and other large companies. This will prevent a lot of them. And that will keep a lot of working class Americans in a MUCH better position than in OTL. OTOH, the companies involved will be badly hurt by this, and will stay uncompetitive, which will eventually lead to rancor with Japan, Germany, and other countries. This rancor will be minor in the long-term, but still could present the risk of trade wars, if not handled well.
Other economic trends: the oil glut of the '80s, the beginning of Boomer investment in stocks and retirement funds, and so on, will lead inflation to decline, just as under Reagan. As interest rates return to lower, though historically still very high, levels, and prices stabilize, Kennedy will get much of the same credit of "restoring prosperity" that Reagan got. This will get him victory in the 1984 elections, in all likelihood beating the aforementioned Ronald Reagan.
Kennedy will still boost defense, but not as much as Reagan. He will probably be reluctant to arm the Afghan mujihaddin, though they will still get a fair amount of support. The Russians will be less worried - economically, or militarily - than in OTL. This will mean that Romanov will probably be selected to replace Chernyenko, instead of Gorbachev. Romanov, despite his name, was a fairly hard-line Communist. Circumstances will still force him to reform, but very slowly, and in ways that have little impact. Relations with the West will improve, however, because the USSR will be just too exhausted and troubled to be able to compete, and will need good relations with America. This desire for good relations will be shared by the Kennedy Administration,and so negotiations will go well, and superpower tensions greatly decline.
1988 will be the year of a moderate Republican, probably Papa Bush. His Presidency will be a lot like a continuation of Kennedy's, though there will be a certain amount of deregulation and increased military spending. However, in OTL, Bush only embraced Reaganomics after becoming Vice President. Here, he stays closer to the center, and so his policies mostly just balance out those of Kennedy. The rather boring conditions of modest prosperity for all will continue. Saddam Hussein will still have fought the Iran-Iraq War, and will still need a good way to pay his war-debts. So, chances are, he still goes into Kuwait in 1990. The US will secretly consult with the Russians before acting, and will receive an assurance that they can indeed act on the matter, provided they don't go all the way to Baghdad. As a result, the Gulf War will happen. A less built-up U.S. military will mean more American casualties, but the "maneuverists" will still have done their work, based on avoiding anything like Vietnam, and so the war will still be an American walkover, and will end almost identically to OTL.
President Bush will not face either the 1990-1992 recession, nor the boom of the '90s we had in OTL. A more stable economy, plus a victorious war, will win him re-election in 1992.
The winter of 1992-93 will be a turning point in the USSR. The economic situation there will have become so bad that demonstrations will grow, demanding economic reforms. Romanov wil try to suppress these demonstrations, which will then trigger riots on a very large scale. The Red Army will be called out to suppress the riots. The generals, however, will be shocked to hear that soldiers are deserting and joining the rioters. This will decide them on a radical course of action. The generals depose Romanov, and replace him with.......Gorbachev. And so Russia will begin moving down the same path as in OTL, eight years later.
A democrat, probably not Bill Clinton, will win the elections of 1996, and probably 2000. And, in 1998, a retired Los Angeles police detective named Mark Fuhrmann will publish a book going into the death of Nixon in detail, and at last proving that it was indeed a suicide, and neither homicide nor accident. This book will be denounced by conspiracy theorists, embraced by many, especially in law enforcement, and ignored by most Americans.