By I-Hsien Sherwood (i.sherwood@latinospost.com) | First Posted: Apr 02, 2013 08:02 PM EDT

While the Senate seems to be moving steadily toward the release of a  bipartisan immigration reform bill, one of its biggest proponents - Marco Rubio -- seems to be losing his nerve. But why?

Over the weekend, Rubio, the Cuban-American senator from Florida and long-time proponent of immigration reform, issued a statement cautioning his fellow senators against moving too hastily toward reform.

"Excessive haste in the pursuit of a lasting solution is perhaps even more dangerous to the goals many of us share.  We owe it to the American people to get immigration reform right this time, so that future Congresses and future generations do not face the broken system we see today.  A rush to legislate, without fully considering all views and input from all senators, would be fatal to the effort of earning the public's confidence," Rubio wrote, in an open letter to Democratic Senate Judiciary Chairman Patrick Leahy of Vermont, who has been pushing for more progressive immigration reform legislation.

Rubio's letter was released just as the Senate's "Gang of Eight," which includes Rubio, announced they had come to a compromise on the major components of the bill, and just days after business and labor groups resolved a long-standing disagreement over a guest worker program.

Rubio has pushed for immigration reform for years; why is he now urging caution and advocating a series of hearings -- the same obstructions proposed by opponents of immigration reform?

The most likely answer is 2016. Rubio is considered a likely candidate for the Republican primaries ahead of the 2016 presidential election, and he needs to build support among the base of the party, which is traditionally anti-immigration.

Less than 30 percent of Latinos in the country vote Republican, but virtually all of the ones that do will likely support Rubio if he decides to run in 2016. That means Rubio needs to warm up to Republican voters who either don't know who he is or don't like his policies. A recent poll showed that more than 40 percent of Republicans in the country say they've never heard of Rubio.

And those that have may be unwilling to support a candidate who was influential in passing legislation generally viewed as favorable to Democrats. Many Republicans worry that most of the 11 million undocumented immigrants who could gain citizenship because of the reform bill will end up voting for Democratic candidates.

After the painful loss of the 2012 election, the Republican establishment understands that they must rehabilitate their image with Latinos, and that means supporting immigration reform. The chances for passage have never been higher, so it is little risk for Rubio to play the part of concerned nativist. It is a ploy unlikely to change the outcome of the legislation, but it may buy him some favor among more conservative elements in the party.

But you'll never hear him say that.

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