No one was expecting a love fest when Representative Mike Lawler, Republican of New York, faced constituents in his suburban swing district on Sunday night. Still, even he seemed surprised by the night’s first clash — over the Pledge of Allegiance.

“Please tell me you’re not objecting to the Pledge of Allegiance,” Mr. Lawler asked incredulously after some members of the audience inside a high school auditorium audibly groaned when he suggested reciting it.

They acquiesced, and several hundred attendees labored to their feet to say the pledge, but not without indicating why they believed its words had come to ring hollow.

“Authoritarian!” one man yelled, an apparent reference to President Trump.

“Support the Constitution!” bellowed another.

So it went for nearly two hours as Mr. Lawler, one of the House’s most vulnerable Republicans and a potential candidate for governor of New York, faced a torrent of criticism from liberal constituents over almost everything, from Republicans’ multitrillion-dollar tax cut plan to how brightly the room was lit.

It was a scene that has repeated itself across the country over the past two weeks for the small group of Republicans who have defied party leaders’ advice and convened feedback sessions with the people they represent, many of them anxious, angry and primed to vent over a president who they believe is acting with unchecked power.