But his inability to hold his fire on Friday raised fresh doubts among his allies and White House advisers about what he will do next week, when eight witnesses are scheduled to testify in public hearings over the course of three days.

Mr. Trump did not clear his Friday tweet with top White House aides before putting it out, leaving some of his advisers deeply dispirited. Privately, they acknowledged he had done himself damage…

One thing [Republicans] were clear about: They intended to use the same care grilling Ms. Yovanovitch that Republican senators tried to employ during last year’s testimony by Christine Blasey Ford, who accused Justice Brett Kavanaugh of assaulting her when the two were in high school, according to one person close to the House Republican leadership.

Mr. Trump didn’t get the message — and Democrats seized on the political opportunity he handed them. Not long after the president tweeted his thoughts on Ms. Yovanovitch, Mr. Schiff read it aloud, to Ms. Yovanovitch and the cameras.