“We need to be able to depend on these senators that we worked so hard to elect,” said Tomás Robles, an executive director of LUCHA, a civil rights group that knocked on tens of thousands of doors in Arizona for Democrats last year. “If they’re going to act like a moderate Republican, we will remember by the time elections come. We expect them to recognize that Latinos voted overwhelmingly for those two, and we expect them to repay our loyalty.”

For many immigration activists, a sense of pessimism has already begun to sink in. They fear that Democrats will try to strike a deal with Republicans who are unlikely to approve the sweeping changes Mr. Biden has proposed — similar to the strategy that failed during the Obama administration.

Erika Andiola, a Phoenix-based immigration activist, became the first known undocumented congressional aide when she worked for Ms. Sinema in 2013, drawn to what she saw as Ms. Sinema’s intense interest and commitment in the issue. Now, Ms. Andiola said she viewed her former boss as moving to a more conservative stance on immigration — more often emphasizing border security than creating a path to citizenship for the roughly 11 million undocumented immigrants living in the United States.