The Republican tax cut is resulting in tangible benefits for workers more quickly than even many of its supporters expected. Bolstering an already-improving U.S. economy, it is starting to exert an equally powerful influence on U.S. politics.

To be sure, President Donald Trump still suffers from low approval ratings. “Based on approval ratings one year into a first term, Trump is the most unpopular president since at least Harry Truman,” notes Harry Enten of the website FiveThirtyEight today. But there are interesting trends...