It took 15 rounds of votes — and concessions to the hard-right flank of his party — for Mr. McCarthy to be elected speaker in January. The White House sees that as a sign of his weakness, pointing to the slim majority Republicans hold in the House.
Mr. McCarthy’s supporters say they view the process as a sign of his strength and ability to stick things out to get the outcome he desires.
“If Kevin is pleasant and calm and persistent, almost the same principle that he had to endure to become speaker, in the end he’s going to get an amazing amount done and people are going to be surprised,” said Newt Gingrich, the Republican who antagonized and impeached President Bill Clinton as speaker and whose former chief of staff, Dan Meyer, is now Mr. McCarthy’s top adviser.
“He’s a good planner,” Mr. Gingrich added. “That’s what people underestimate about Kevin.”
The relationship has not been without its lighter moments.
On Friday, the two Irish American politicians joked with each other at a St. Patrick’s Day event at the Capitol, with Mr. McCarthy comparing their relationship to that between President Reagan, a Republican, and Speaker Thomas P. O’Neill Jr., a Democrat, who also shared Irish heritage.
“A clash is brewing, people say, between the president and I of what should we do?” Mr. McCarthy said. “What would be the ramifications for the entire nation in the coming months? I think you might be able to settle this for us. Which one of us is more Irish?”
Mr. Biden responded, “there’s no reason we can’t find common ground.”
The president has in the past tried to indulge Mr. McCarthy’s love of the trappings of congressional leadership. (He enjoyed traveling aboard Air Force One with Mr. Trump.) When Mr. McCarthy was invited to the state dinner in honor of Emmanuel Macron of France, he called the White House asking for an invitation for his mother. The president quickly obliged, according to two people familiar with the call.