A tweet Friday, in which Trump threatened to veto the spending bill, also underscored another tenet of Trumpism — a state of continuous uncertainty about where he will land on key policies. In the tweet, Trump said he was frustrated with the legislation both because it “totally abandoned” young undocumented immigrants known as “dreamers” (long a Democratic priority) and because it failed to “fully” fund his controversial border wall (now a Republican priority).

“There has certainly been a wholesale repudiation of many core principles that have guided the Republican Party’s thinking over the years,” said Eswar Prasad, a professor of trade policy at Cornell University. “Their willingness to accept certain victories on their agenda in return for the acceptance of Trumpism more broadly — that seems to be the guiding principle of Republican Party leaders.”…

“I would argue that Trump is more a reflection of where the voters are today,” said Barry Bennett, a former Trump campaign adviser. “I don’t think he persuaded them into these stances. That’s where they were. He’s merely being a mirror to them. . . . He heard what the voters were talking about, what they feared, the pain that they had, and he immediately championed it.”…

An NBC News/Wall Street Journal poll last week illustrated the point, finding that 59 percent of registered Republican voters said they consider themselves more a supporter of Trump than the Republican Party.