The May Revolution
When the news of the fall of the Junta of Seville arrived in Buenos Aires in the middle of May aboard British ships, rumors immediately started spreading in the city about the implications despite the best efforts of colonial authorities. Chief among the rumors was that - given the fall of the Junta - Cisneros’ position as Viceroy teetered on the brink. After all, if the body that had appointed him Viceroy had ceased to exist, didn’t that logically mean that he had thus ceased to be Viceroy?
Painfully aware of just how precarious his position was, and hoping to both save himself and forestall the proliferation of cabildos in open rebellion like the ones he’d faced upon his appointment, Cisneros attempted to thread the needle but time was against him: local patriots like Belgrano and Castelli had heard the rumors almost as soon they arrived in the city, and his Cisneros’ authority eroded more every day he attempted to delay confronting the issue. By the 20th, his position became untenable: the criollo regiments formed to combat the British invasions and which had already proven their importance in Buenos Aires politics by helping put down the Alzaga mutiny, refused orders to defend him and Cornelio Saavedra went so far as to suggest his resignation.
Cisneros could put it off no longer and agreed to demands from local leaders that an open cabildo should be held. But the delay - both in publicly recognizing the news of the fall of the Central Junta and in convening a cabildo to deal with the fallout - had led to a radicalization of local sentiment: a mob threatened to storm the Cabildo’s first regular session the next day, fearing that Cisneros had only agreed under duress and was plotting to go back on his word, and the crowd would refuse to vacate the square until the Cabildo produced a guest list for the open session.
With the list published, criollos worked tirelessly, both to procure their own invitations and to ensure that they would have full control over proceedings the next day. A sympathetic printer made sure to produce surplus invitations for distribution among the locals, while criollo leaders visited the troops to keep them on their side. When the Cabildo finally opened the next day, criollos made sure they commanded a majority inside, while armed sympathizers held the square and stood ready to intervene if somehow their majority faltered. But the most radical of the criollos, spearheaded by Mariano Moreno, did not trust Cisneros or the Cabildo: the former had already tried to manipulate the crisis to his own benefit, whereas the latter - the ongoing open session notwithstanding - had been reticent to move on its own and Moreno was convinced that their acceptance of the open Cabildo was under duress as well, so he conferred with his fellow revolutionaries the night before and hatched a plan.
Moreno feared that Cisneros had no intention of stepping down, and worse, that his allies in the Cabildo could command a plurality if not a majority even if he were forced to resign given the divisions in the anti-Cisneros camp. While they were certain they had the votes to remove the Viceroy, what came next remained uncertain, so Moreno had an idea: force the issue of the Viceroy to a vote early, then use the rest of the debate to try and unify around an alternative.
Benito Lue y Riega, bishop of Buenos Aires and speaking in support of Cisneros and the ratification of his position, set the tone for the debate on the 22nd by stating plainly that “not only is there no reason to get rid of the Viceroy (...) America should only be ruled by the natives when there is no longer a Spaniard there”. Castelli would seize on the bishop’s statement, and would end his speech with a short proposal, which likewise served as a signal for Belgrano - perched at the window - to wave for the crowd to once again chant against Cisneros and demand his resignation: “I suggest we vote immediately, for all else rests upon this decision: shall we ratify Cisneros as Viceroy, or shall this body decide our fate”.
Control of the mob would once again prove decisive for the patriotic cause, as the Cabildo bowed to the pressure and put the matter of Cisneros’ position up for a vote early in the day: with 125 votes against 99, the Cabildo voted to remove Cisneros as Viceroy and assume the authority to replace him, and he abandon the meeting in dismay as the crowd outside cheered. As the people in the square calmed down, the Cabildo resumed its debate in a tense atmosphere, as Cisneros’ absence left only their divisions over what should take his place.
During the rest of the day, several attendees would make their own proposal: the most conservative members hoped to maintain the status quo as best they could, and proposed simply that the Cabildo rule in the interim but ultimately appoint or accept a new viceroy; Cisneros’ supporters for their part sought a compromise and proposed that the deposed Viceroy continue with a new title, but this was fiercely resisted by the revolutionaries and the Cabildo was hesitant to force the issue with the crowd still outside. At the end of the day, a consensus seemed to form over the proposal that obtained a plurality of the votes: proposed by Saavedra, it empowered the Cabildo to form a governing Junta and appoint its members.
When the ordinary Cabildo reconvened on the 23rd, they set about carrying out the decision of the previous day’s session. Despite the explicit rejection of Cisneros, its members were hesitant to dispense with him entirely, and as they debated the composition of the new Junta, they resolved to name the former Viceroy as its president in an effort to preserve the status quo as best they could. They hoped that by completing the Junta with a plurality of patriots like Saavedra, Castelli and Solá they could mollify the revolutionaries, but as the events of the 24th would show, they had severely underestimated the opposition to Cisneros.
When the composition of the Junta was announced early on the 24th, the reaction of the crowd headed by French and Beruti - many of them members of the militia and congregating in the square armed and irate - forced the Cabildo’s members to retreat back into the building and hide from hurled insults and stones. Cisneros, attempting to exercise the authority the Cabildo had conferred to him, summoned Saavedra, Huidobro and Rodriguez and ordered them to disperse the crowd, hoping that Saavedra - the most prominent of the three - would acquiesce and force the other two to do so as well by virtue of his inclusion in the named Junta. Instead, Saavedra rebuffed his command, and all three commanders repeated the suggestion they’d made to Cisneros earlier in the week: resign, because even if they were willing to order their soldiers to disperse the crowd, they would simply mutiny and join the mob.
The Cabildo attempted to negotiate with the crowd and its leaders, but they refused to accept any Junta presided by Cisneros. These failed negotiations, combined with Cisneros’ intransigence in the face of mass opposition, only served to radicalize the revolutionaries, and as the former Viceroy attempted to save his position, patriot leaders began collecting signatures from among the crowd and draft a manifesto.
The standoff lasted for most of the day, but the steadfast refusal of the city’s military commanders to order their forces to intervene on his behalf forced Cisneros’ hand: he announced to the commanders that he intended to resign, and they took the news to the crowd that - once more - greeted the news with glee.
The Cabildo however would not be so easily swayed: they met once again early on the 25th and promptly voted to reject Cisneros’ resignation, stating bluntly that whatever the mob might claim, the only thing that had been clear from the votes on the 22nd was that it was the Cabildo’s prerogative to name the Junta, so they ratified his designation and summoned the top military leaders of the city to order them to carry out their duty and defend the government it had appointed. The day had dawned overcast, but a crowd began to gather outside the building despite the inclement weather, and soon it swelled to a mob that threatened to break down the doors.
When it became clear that the Cabildo refused to budge, the crowd surged forward and forced the exterior doors open, forcing them to open negotiations with its leaders; despite the Cabildo members’ pleas for calm and for the crowd to accept the will of the Cabildo - which they again stated was fully in keeping with the letter of the proposal that had been voted on the 22nd - the crowd grew more agitated at the protracted negotiations, and their warnings that Buenos Aires could not unilaterally upend the entire political order of the Viceroyalty fell on deaf ears.
Defeated, the Cabildo finally accepted Cisneros’ resignation and agreed to name a new Junta, but by then the revolutionaries’ patience had run out: they demanded that the Junta be elected by the people. The Cabildo scoffed at first, but with the angry mob still gathered outside, the negotiators calmly told them that they could hardly contain the passions of the crowd as it was, and ultimately they could not guarantee the safety of the Cisneros or the Cabildo if they refused. Hoping to buy time for Cisneros to gather support and summon more loyal troops, they agreed on the condition that the leaders of the revolutionaries presented their proposal in writing.
Much to their dismay, the revolutionaries had come prepared: Antonio Beruti produced the document, which carried the signature of the most prominent patriots in the city as well as hundreds more unidentified signatures purported to belong to other notable members of society and of the different militia regiments that had proven decisive in Cisneros’ downfall. The Cabildo members asked for more time to deliberate, but Beruti and his compatriots refused: too much time had already been lost to the Cabildo’s spurious efforts to circumvent the will of the people. If they did not accept the terms, the negotiators would leave and return with a better armed crowd.
And so, as the sun broke through the clouds in the afternoon of May 25, 1810, the Cabildo read out the proclamation of the country’s first revolutionary government, and the crowd cheered as the composition of the Junta was announced. A dejected Cisneros fled to his house to send a messenger to his predecessor in Córdoba as Cornelio Saavedra, commander of the Regiment of Patricians, was introduced as President of the Junta and was joined on the balcony by the rest of its members: Manuel Alberti, Miguel de Azcuénaga, Manuel Belgrano, Juan José Castelli, Domingo Matheu and Juan Larrea, and secretaries Juan José Paso and Mariano Moreno. The May Revolution had begun.
Litograph of the first patriotic government
 Moreno was amongst the most radical of the revolutionaries, and IOTL had good reason to be suspicious of the Cabildo’s intentions, as their insistence on designating Cisneros as the president of the Junta meant to replace him showed. IOTL, he expressed his concern after the open session, but ITTL he’s a bit more machiavellian and hatches a plan to try and set the tone of the session early on.
 The first PoD: IOTL, the debate lasted all day long, and the voting was tallied after all the proposals had been presented, running the gamut from ratifying Cisneros to convening a Constitutional Assembly. ITTL, the revolutionaries force the issue early and demand that the vote be held immediately with the help of the raucous crowd outside (which had gathered IOTL, but was not signalled to intervene).
 The tally IOTL was 155 to 69; ITTL, the vote is closer because the issue of the removal of the Viceroy is being forced early, and while there was an overwhelming majority in favor of deposing Cisneros, it may not have been quite as overwhelming if the 30 votes for Huidobro’s position didn’t hope to score a plurality in favor of having their own candidate take his place.
 The second PoD: both sides are slightly more radical than their OTL counterparts, and given the explicit repudiation of Cisneros on the 22nd, the Cabildo’s decision to name him president of the Junta is even worse received ITTL - to the extent that the rest of its members don’t swear loyalty to it before being forced to resign later that night. Another key detail is that the revolutionaries have had a lot more success with their use of the mob, which is shown by their confrontation with the Cabildo early in the morning.
 A third PoD: IOTL, it took the revolutionaries several hours to gather the signatures and present the document. ITTL, its most radical members have been preparing for this precise moment since the day before, and Beruti arrives at the negotiations with the document already prepared.