Two realities shape the debate over immigration reform: No bill is likely to pass without the expressed support of Sen. Marco Rubio (R-Fla.), but even Rubio’s endorsement may not be enough to assure passage. For Rubio, the political stakes of both sides of the equation are huge.

Immigration reform is one of President Obama’s most important second-term priorities, but for now the president has been relegated to a secondary role in the debate. Because his views are anathema to conservatives, the less he says about the bill, the better may be its chances of passing. In Obama’s place, Rubio has emerged as the most significant public voice on the issue.

The immigration bill began its legislative journey last week when the Senate Judiciary Committee started to mark up the proposal developed by the bipartisan Gang of Eight, of which Rubio is a member. Hundreds of amendments may be considered, and the opening day highlighted conservatives’ determination to toughen provisions related to border security. Resistance to the current bill will be even fiercer in the House.

Rubio is not a member of the Judiciary Committee but nonetheless plays the pivotal role for two reasons: He is the most prominent trusted conservative who advocates a path to citizenship for the millions of illegal immigrants in the United States, and he serves as a conservative arbiter of the line between legitimate changes designed to toughen the bill and conservative poison pills designed to kill it.

Immigration reform could be a crucial moment for Rubio’s party. Republicans know they cannot win the presidency in the future without significantly improving their level of support from Hispanics. Passage of immigration reform will not solve all the party’s problems with Hispanic voters, but it would remove one stigma that has prevented GOP candidates from gaining a fuller hearing in the Hispanic community.

See which amendments were adopted into the immigration bill

The issue divides the Republican coalition, but there is far more support within the party for comprehensive reform than there was in 2007, when then-President George W. Bush tried and failed to get it enacted. When the conservative Heritage Foundation issued a report critical of the reforms last week, other conservatives attacked its findings and methodology.

There are a host of reasons why Rubio enjoys the standing he does on this issue. He is Cuban American and the party’s most prominent Hispanic elected official. He has impeccable conservative credentials, having been propelled to office with the strong support of tea party activists in Florida and around the country. He has considerable skills as a communicator. And he is expected to be among those seeking the Republican presidential nomination in 2016.

But in taking on immigration, he has put himself in an unusual position. By the end of this year, he could find himself in the minority among House and Senate Republicans on the issue, if he chooses to continue to support the bill. Not many presidential candidates start out a campaign with a signature issue that has been rejected by a majority of the elected officials and much of the base in his or her party.

Offsetting that potential problem is the fact that other prospective 2016 candidates have expressed support for comprehensive immigration reform, among them former Florida governor Jeb Bush, Sen. Rand Paul (Ky.), Rep. Paul Ryan (Wis.), New Jersey Gov. Chris Christie and Wisconsin Gov. Scott Walker.

Rubio advisers say his role has been clear to them from the start. His support for reform is genuine and grows out of his own experience in the immigrant community. He concluded that if there were to be any chance of passing a bill, he would have to play a highly visible role — not as conservative window dressing or as a way to rebuke his party, but because of his credibility as someone who could work behind the scenes to move the bill to the right and to reassure fellow conservatives as the debate unfolded.

Conservative media’s role

In sometimes giving voice to conservative reservations, Rubio has been seen as a wavering advocate who may be looking for a way out of the debate. Advisers say he is as committed as ever to finding compromises that will allow a bill to pass and to continuing to develop trust and goodwill among conservatives as he works to do that.

When immigration reform died in 2007, conservative talk radio helped to kill it. At the peak of the debate in 2007, according to a study by the Pew Research Center’s Project for Excellence in Journalism, conservative talk shows devoted about a quarter of their air time to the immigration debate.

Rubio has worked assiduously to assuage the concerns of the most influential voices, in public appearances and in private phone calls and conversations. He has spoken regularly with people such as Rush Limbaugh, Mark Levin, Sean Hannity and Laura Ingraham to make that case.

His advisers closely monitor how much time these hosts are devoting to immigration, compared to six years ago, and they are heartened that the volume is much diminished, even if some oppose what he is doing. Over the past few weeks, Limbaugh was giving the issue an average of about 12 minutes a day, Hannity 6 minutes, Levin 14 minutes and Ingraham 35 minutes, according to analysis provided by a Rubio adviser.

So far, Rubio has managed to avoid the kind of criticism from conservatives that was heaped on Sen. John McCain (R-Ariz.) when he led the earlier fight for comprehensive reform. Limbaugh recently called Rubio “a thoroughbred conservative” and sought to reassure a caller who shared Limbaugh’s opposition to a path to citizenship for illegal immigrants by saying, “Marco Rubio is not out to hurt this country or change it the way the liberals are.”

Gathering votes

At this point, according to one count shared by an advocate of reform, there are only four certain Republican votes for the measure — those of Rubio, McCain, Sen. Lindsey O. Graham (S.C.) and Sen. Jeff Flake (Ariz.). An additional five senators are currently considered possible supporters. How many more Senate Republicans the bill can attract will depend on what emerges from the amending process. The size of an eventual Senate majority will influence what happens in the House.

The process may continue late into the year, and its success will depend heavily on how effective Rubio is in reassuring enough conservative Republicans that it is in their interest, and the country’s, to find an acceptable solution.

What is ironic is that Obama, who as a freshman senator took over the leadership of his party to become president, now finds his key initiative in the hands of a freshman senator of the opposite party who could become the GOP standard bearer in the contest to succeed him in the next election.

For previous columns by Dan Balz,go to