His survival skills may be put to a new test as he fights back against the term limits proposal, which is subject to a vote of the entire caucus when the new Congress convenes in January. The debate will pit old-school Democrats like Mr. Hoyer, who derive their power from the seniority system, against newcomers, who want to shake things up.

“Steny entered the political scene at a time when Democratic Party politics was much more conservative and traditional in how it operated,” said Representative Jamie Raskin, a fellow Maryland Democrat, adding, “One of the last great challenges of Steny’s career is to figure out how to incorporate the surge in progressive feeling in our party.”

Mr. Hoyer’s stock in trade is his ability to cultivate allies across the Democratic spectrum (not to mention lobbyists and donors), and he is busy making new friends on the left. Among them is Alexandria Ocasio-Cortez, the progressive firebrand from New York, who at 29 is half a century his junior. He dropped in to see her at a cafe in Queens on Halloween, the first time they had met.

“I remember feeling very pleasantly surprised,” Ms. Ocasio-Cortez said.

But while he may have left her with the impression that he will embrace her vow to make waves, in the interview, Mr. Hoyer was more cautious. He took a dim view of Ms. Ocasio-Cortez’s decision to join environmental activists at a protest in Ms. Pelosi’s office.

“I was a little bit surprised, but you know, she’s gung-ho, she’s full of vim, vigor and vitality,” he said, adding tartly, “One could say there are other ways to make a point.”

Like Ms. Pelosi, Mr. Hoyer raises millions of dollars for Democrats — more than $10 million in this election cycle alone — and crisscrosses the country campaigning for them. Unlike her, he has not become the subject of Republican attack ads and is welcome in districts across the country. If Ms. Pelosi is the public face of the caucus, he is the “member’s member,” guiding younger colleagues on everything from hiring decisions to committee assignments.