His words have been turned into television commercials by groups on both sides of the issue. And no one has taken on more friendly fire. Mr. Rubio has been attacked at Tea Party rallies (his name elicits boos), on conservative radio (“a piece of garbage,” Glenn Beck called him) and in National Review (“Rubio’s Folly,” declared a recent cover).

Still, running interference on Mr. Rubio’s behalf is fraught with risk for conservative groups, who are going against many in their own base.

“We know that there’s a lot of folks on both sides,” said Tim Phillips, president of Americans for Prosperity. “But I think the vast majority of people appreciate the fact that Senator Rubio is doing what he thinks is best for the country. And that he’s doing it in an open and honest way.”

Mr. Phillips declined to discuss any implications for Mr. Rubio and 2016, but said, “We think that he’s got a bright future within the movement, and in whatever he chooses to do down the road.”

Many other big players in the conservative movement would like to keep that future bright as well.

Ralph Reed, president of the Faith and Freedom Coalition, invited Mr. Rubio to speak to several hundred of his members at a conference in Washington last month. Mr. Reed, who has made clear that he believes the Senate immigration bill that Mr. Rubio helped write is too lenient, described the crowd as right-leaning, by Republican standards. “Not the Chamber of Commerce variety,” he noted wryly in an interview.

But when he introduced Mr. Rubio, he offered nothing but effusive praise. “We’re proud to count him as our friend because he has not forgotten who got him here,” Mr. Reed told the crowd, which applauded politely. “He has not forgotten who he is.”

Weighing heavily on conservative leaders is a reminder of how immigration policy bedeviled Mitt Romney last year. His “self-deport” comments about what should happen with the 11 million immigrants living illegally in the United States became an easy punch line for Democrats and helped drive Latinos even farther away from the Republican Party.