The cases were part of a New York Times review of more than 75 indictments of people charged with threatening lawmakers since 2016. The flurry of cases shed light on a chilling trend: In recent years, and particularly since the beginning of Mr. Trump’s presidency, a growing number of Americans have taken ideological grievance and political outrage to a new level, lodging concrete threats of violence against members of Congress.

The threats have come in almost every conceivable combination: Republicans threatening Democrats, Democrats threatening Republicans, Republicans threatening Republicans. Many of them, the review showed, were fueled by forces that have long dominated politics, including deep partisan divisions and a media landscape that stokes resentment.

But they surged during Mr. Trump’s time in office and in its aftermath, as the former president’s own violent language fueled a mainstreaming of menacing political speech and lawmakers used charged words and imagery to describe the stakes of the political moment. Far-right members of Congress have hinted that their followers should be prepared to take up arms and fight to save the country, and in one case even posted a video depicting explicitly violent acts against Democrats.