Reid has promised a Senate vote this year on a small piece of immigration legislation known as the DREAM Act, which would give hundreds of thousands of undocumented immigrants a conditional path to legal residency.
"The answer is yes," Reid told Univision host Jorge Ramos in October when pressed about whether there will be a vote. "I have the right to bring that up any time I want."
As Congress reconvenes this week for the final session of the year, Reid now has roughly a month to make good on his promise.
Many immigrants and immigrant advocates, particularly Hispanics, have been disappointed by Congress' inaction on legislation to address the situation of millions of the country's undocumented immigrants, particularly those who are young children.
However, Republican opposition to efforts to legalize undocumented immigrants, a packed end-of-year legislative agenda and a bleak track record for controversial bills during lame-duck sessions all cast doubt on chances of the bill's passage this year.
The DREAM Act would grant legal status to immigrants who complete college or at least two years of military service and maintain "good moral character." It would apply to immigrants younger than 36 years old who arrived in the U.S. illegally as children under the supervision of their parents.
"We are very confident this will come up for a vote," said Flavia de la Fuente of the adovacy group DreamActivist.org. "We are confident that the American people and that the moderate GOP will make the right choice when it comes to investing in the future of this country."
Reid attempted to attach the measure as an amendment to the defense authorization bill in September, drawing intense protest from Republicans, who accused the Democrat of playing pre-election politics.
Ultimately, Republicans blocked the effort to bring the defense bill to the floor for debate, precluding a chance of adding the DREAM Act. The bill also included a repeal of the military's "don't ask don't tell" policy.
"We're going to vote on the Dream Act; it's only a question of when," Reid said after the vote. "It's a question of fairness. This is not the end of this."
Many activists on both sides of the issue agree, however, that chances of the bill's passage are only going to grow dimmer with an influx of Republicans set to join the House and Senate in January.
Roy Beck, president of Numbers USA, a group that favors tighter immigration controls and supports Republicans' efforts to block the DREAM Act, said the measure is flawed.
"Some of these [immigrants] are compelling cases, no doubt about it," said Beck. "But you've got to draw some lines a lot narrower than the DREAM Act draws them. This is about giving millions of illegal aliens permanent work permits, and I don't think in this economy that this is a very happy time to be doing that."
President Obama supports the legislation, as does Defense Secretary Robert Gates, who says it would help recruitment, and Education Secretary Arne Duncan, who says it's "the right thing to do for our country."
But it's unclear whether the administration will push behind the scenes in the weeks ahead to make it a legislative priority. The Congress already faces challenging debates over whether to extend the Bush tax cuts, fund the federal government through 2011, and approve a controversial defense spending bill.
"The president supports the DREAM Act and I support the DREAM Act. The president supports immigration reform, and I support immigration reform. And how Congress takes that up is for the Congress and the leadership to decide," said Homeland Security Secretary Janet Napolitano in September.
The DREAM Act has received some bipartisan Senate support in the years since it was first introduced in 2001. It was approved as part of immigration reform bill in 2006, but the package later failed in the House. In 2007, the Act was filibustered when it came up for an up-or-down vote.
Speaker Nancy Pelosi has decided not to list DREAM Act as a priority for this week, a senior Democratic aide told ABC News. But it could come up after Thanksgiving.
According to the nonpartisan Migration Policy Institute, about 2 million of the nearly 11 million undocumented immigrants currently living in the U.S. could be eligible for legalization under the DREAM Act.
The group also estimates, however, that only 825,000 of those immigrants would ultimately take advantage of the law if it were enacted.
ABC News' John Parkinson contributed to this report.