Trump keeps killing his own momentum. It’s a tragedy.

Then, to add to the PR disaster, Trump declared at what was supposed to be an event highlighting his tax reform success that Democrats who refused to stand and applaud during his State of the Union were “un-American” and “treasonous.” He was joking, of course, but it was a really bad joke — and gave the media the excuse to gin up the outrage machine over Trump’s comment. Again, Democrats quietly celebrated. Until that moment, they had been widely criticized for their disrespectful performance on the House floor, which had alienated millions of Americans watching the president. Even my liberal Post colleague Dana Milbank called the Democrats’ behavior “embarrassing.” Now, with a single misbegotten turn of phrase, Trump had turned them from petulant protesters into principled defenders of the First Amendment.

These mistakes were tragic, because Trump’s address seemed to reach and win the approval of many Americans who like his first year’s accomplishments but don’t approve of him, including millions of independents and Democrats. With his speech, he got them to give him a second look. In the days that followed, he needed to stay on message and keep winning them over with smart speeches putting detail onto the policies he laid out in his State of the Union. He could have hit the hustings to talk about his very generous immigration plan to give 1.8 million “dreamers” a path to citizenship and challenged reluctant Democrats to come to the table. He could have given speeches about his proposals for education, tackling the opioid crisis, and “right to try” legislation he endorsed to give dying Americans a chance to save their lives using experimental treatments. He could have won over independents, and even some Democrats, and expanded his base of support. Instead, he changed the topic to Russia and made a cringe-inducing joke about “treason,” and millions thought to themselves: There he goes again.