John Quincy Adams negotiates the exile of the Decembrists, their families, any other soldiers under the officers' command, and those soldiers' families to the United States. Their middle-class supporters follow suit in what amounts to a total emigration of some 70,000 people (3,000 Decembrists * 5 family members + maybe 50,000 middle class supporters).
Following the Polish Uprising of 1830, the Tsar decides "hey deporting people to America is a great idea" and sends 500,000 people (Polish/Lithuanian/Ruthenian Soldiers, their families, etc) to America. Maybe 50,000 of these people are Ruthenes/Ukrainians.
Now there's probably 120,000+ Orthodox Christians in the US by the mid-1830s. Going to America for freedom has become an exit strategy in Russia for dissidents as well, so there continues to be a slow trickle over. Americans generally don't have much issue with the new folks because they're disproportionately nobles, officers, and middle-class types who are largely beneficial. Over time these Orthodox Russians and Ruthenes end up growing to some 2% of the population and many Americans decide "hey their religion seems pretty nice" and thus Orthodoxy grows into being 4 or 5% of the population. A Patriarchy of North America is established as well, separate from Moscow and Istanbul, and thus the American Orthodox Diocese is seen as more "Kosher" by Americans than Catholicism.
Later on, a lot of the Orthodox Christian Levantine Arabs who went to Latin America (Brazil, Argentina, Chile, etc) go to the US instead, buttressing the Orthodox population up to 8-10% of the population.