“What still rubs a lot of the opponents the wrong way is that Rubio and his team engaged in all the evasions and misleading salesmanship that inevitably come with this sort of legislation,” said Rich Lowry, the editor of National Review, citing, for instance, the strength of provisions requiring that immigrants learn English. He received updates by phone and in person from Mr. Rubio throughout the process.

Slowly, Mr. Rubio began publicly undermining his own legislation, at least in the eyes of his colleagues and their staffs.

Gang of Eight staff members said they had seen two competing factions (“Jekyll and Mr. Hyde,” quipped one) in Mr. Rubio’s operation. There was the version they saw in private meetings and Mr. Rubio’s policy team, always working hard and well prepared. At the same time, there was the public Mr. Rubio and his communications and political shop, subtly casting doubt on the bill.

But the bill’s supporters needed him. And whenever he was pressed, Mr. Rubio argued that, as the senator with Tea Party credibility whose job was to sell the plan to the conservative base, he needed some cover and distance.

“I don’t know what you want me to do,” several Senate aides recalled Mr. Rubio saying. “We’re getting a lot of flak from the right wing, and this bill isn’t going anywhere if I can’t sell it.”