[...]the Biden administration mounted a sustained pressure campaign aimed at Brazil's military, which began as early as 2021. The effort, as first reported in Folha de São Paulo and also covered by Foreign Policy, involved explicit public warnings by U.S. senators about not respecting election results as well as continuous back-channel conversations to make clear that a democratic rupture would leave Brazil isolated on the international stage—and lead to a downgrade of U.S.-Brazil security cooperation, which is highly valued by Brazil's military establishment.
The campaign involved the U.S. White House, State Department, CIA, Senate, and—notably—the Pentagon. In retrospect, including that last agency may have been the Biden administration's most decisive move. U.S. Secretary of Defense Lloyd Austin was employed as Biden's chief public emissary to Brazil's generals. It was a natural choice given the tense relationship between Biden and Bolsonaro, the latter of whom followed Trump's lead in parroting falsehoods about supposed fraud during the 2020 U.S. presidential election. Austin was also a more credible interlocutor since Brazil's military was the intended target of the U.S. campaign.
The sheer number of U.S. actors involved in the campaign meant that, for much of 2022, many Brazilian government officials visiting Washington received an unambiguous message from the U.S. government about the need for Brazil's military officers to respect the electoral process. Shortly before Brazil's election, the U.S. Senate passed a resolution calling on Brazil to ensure the vote is "conducted in a free, fair, credible, transparent, and peaceful manner." In order to minimize the risk of a coup, Biden, along with numerous Western allies, publicly congratulated Lula for his victory in the hours after the official results were made public.
Respecting democratic norms is very important. That said, I don't know that citing US imperialist clout is the best way to get the so-called American "left" behind the incumbent administration if said voter were already looking elsewhere or not planning to vote