The findings are a red flag for Trump, whose core support has held remarkably solid through firestorms over his personal behavior, his provocative rhetoric, and his most controversial actions in the White House. But he has become increasingly embattled over his role in fueling the Jan. 6, 2021, assault on the Capitol, his alleged mishandling of sensitive documents when he left the White House, and investigations into efforts to overturn the results of the 2020 election.