On Twitter, and at the top of his meeting with small-business leaders, President Trump could not resist himself. He’d seen Senate Minority Leader Charles E. Schumer tear up talking about the travel ban on some refugees and immigrants on Sunday, and he didn’t buy it for a second.

“I noticed Charles E. Schumer yesterday with fake tears,” Trump said Monday, as some of his communications advisers chuckled. “I’m gonna ask him who is his acting coach because I know him very well, I don’t see him as a crier. If he is, he’s a different man. There’s about a five percent chance that it was real, but I think they were fake tears.”

Schumer’s office declined to respond to Trump. In just a few sentences, Trump seemed to be ditching a relationship he’d cultivated for years — one that had been problematic during the 2016 primaries. Trump had donated a total of $7,900 to Schumer’s Senate campaigns — which, after his first election in 1998, were not very competitive. In the 2006 election cycle, when Schumer ran the Democratic Senatorial Campaign Committee, Trump had given it $5,000.

In 2015 and 2016, when 16 Republicans were trying to defeat Trump in the primary, this was a sore point. Trump’s support for Schumer, they said, indicated that he would sell out conservatives whenever the chance arose.

“Mr. Trump’s pitch to the Washington establishment is he’s a dealmaker,” Sen. Ted Cruz (R-Tex.) said at a news conference before the Iowa caucuses. “He’ll go and cut a deal with Chuck and Nancy [Pelosi] and those deals and will do exactly what John [Boehner] and Mitch [McConnell] have done.”

Cruz, one of the last candidates in the race against Trump, wielded the Schumer donation like a club against Trump. He swung and missed at a January 2016 debate, when he accused Trump of holding “New York values” and Trump defended himself by insisting that Cruz had demeaned the people of a great state. Among the New Yorkers defending Trump on that point — Charles E. Schumer.

“I’m a Democrat, but Donald Trump did a very good job defending New York,” Schumer told Republican businessman and 2013 New York mayoral candidate John Catsimatidis on his radio show. “I’d like Ted Cruz to go talk about New York values to the firefighters who rushed to the towers on 9/11, and the police and EMTs, to the brave New York police officers who keep our streets safe.”

Since Trump’s election, Schumer’s tone changed dramatically — but not completely. The Democratic leader took heat from left-wing activists for saying that Trump might win his support if he was serious about passing an infrastructure bill. That got bigger headlines than Schumer’s criticisms of Trump and promises that Democrats would stand up to him, which on the left were seen as middling.

Since the “tears” comment, however, Schumer has pledged to vote against five more of Trump’s nominees. Trump’s counterpunch tactics, of mocking opponents until they can be defeated and welcomed back into the fold, worked remarkably well during the Republican primary. Deployed against Schumer, it’s not clear what those tactics have gained.