Republican leaders had muscled through their failure to repeal the Affordable Care Act, punted on the perennial brinkmanship over the debt ceiling and finally reached the one issue that all of the party’s factions wanted to be on, tax reform.

Then, over a Chinese dinner at the White House with the two top Democrats on Capitol Hill, President Trump threw that momentary sense of satisfaction into disarray, forcing Republicans to confront the subject that packs more emotional and political force than anything they had on their busy agenda: immigration.