Senate debate on a far-reaching immigration bill is becoming a test of Sen. Marco Rubio’s influence over fellow Republicans, as the Florida conservative works to sell GOP lawmakers on landmark legislation that also may help determine the fate of his presidential ambitions.

Rubio, a tea party favorite who’s acted as the bill’s emissary to the conservative community, has spent recent weeks meeting individually with Republican senators to discuss strengthening the legislation in ways that could get them on board. That included supporting changes sought by Sen. John Cornyn, R-Texas, who outlined a tough border security amendment Wednesday in The Dallas Morning News.

Rubio was to address House conservatives Wednesday, and he’s been promoting the legislation with numerous TV and radio appearances. On Tuesday alone, he showed up on Fox News Channel, CNBC and Hugh Hewitt’s talk radio show.

At the same time he’s been making immigration advocates uneasy by issuing demands for stronger border security provisions in the legislation, including giving Congress more authority to write a border security plan instead of the Homeland Security Department. Rubio says he won’t support the bill without such changes, and it won’t be able to pass.

“If we can pass a measure that ensures that we will never again have another wave of illegal immigration, I believe we will have immigration reform. And if we do not pass that, if that does not happen, I believe there will not be immigration reform. It’s as simple as that,” Rubio said on Hewitt’s show.

For Rubio, it’s part of the balancing act he’s been performing all year since joining more seasoned legislators like Sens. John McCain, R-Ariz., and Chuck Schumer, D-N.Y., as part of the so-called Gang of Eight senators who authored the immigration bill. His challenge is to maintain the support of the tea party backers who lend him credibility and leverage in the immigration debate, while also getting credit for pushing a landmark piece of legislation that’s opposed by many in the tea party but is a priority to the Latino voters who increasingly help determine the outcome of presidential elections.

“He speaks their language, he’s been one of them this entire time, he was a tea party favorite from the beginning,” said Rebecca Tallent, director of immigration policy at the Bipartisan Policy Center, and a former aide to McCain. “Will he take some responsibility if they can’t build a large coalition in the Senate? Absolutely. But so will the rest of the gang members.”

The legislation, a priority for President Barack Obama, aims to boost border security and workplace enforcement, transform legal immigrant and worker programs and put some 11 million immigrants here illegally on a path to citizenship.

As the only author of the bill with the bona fides to sell it to conservatives, Rubio’s been seen for months as key to its passage.

In recent weeks, Rubio’s efforts have been largely behind the scenes as the Senate Judiciary Committee, of which Rubio is not a member, debated the legislation before approving it on a bipartisan vote. Now, with the full Senate set to take up the bill next week, Rubio’s about to assume a more public role. His performance may spell success or failure for the bill and for his own political prospects as a potential presidential candidate in 2016.

Rubio and other backers of the bill are working to build support for the legislation in the Democratic-controlled Senate, convinced that a resounding vote that includes many Republicans would pressure the GOP-led House to act.

But for now, while support is all but assured from a large majority of the Senate’s 54-member Democratic caucus (including two independents), only Rubio, McCain and the two other Republicans who helped write the bill — Lindsey Graham of South Carolina and Jeff Flake of Arizona — are definite “yes” votes among the GOP. On “Fox and Friends” on Tuesday, Rubio said the bill wouldn’t have the 60 votes needed to pass the Senate without improvements.

Working with a list of 15 to 20 Republican senators who potentially could be persuaded to vote for the bill, Rubio’s been meeting individually with lawmakers to hear their concerns. He supported Cornyn’s efforts on an amendment to enact tough new border requirements, including a biometric exit system at all airports and seaports, before any immigrant here illegally could achieve permanent legal residence. Sens. Tom Coburn, R-Okla., and Rob Portman, R-Ohio, said Tuesday they’d met with Rubio to discuss their concerns over border security and enforcement, and Portman said he was weighing amendments to address them.

Sen. Dean Heller, R-Nev., wrote an opinion piece in the Las Vegas Review-Journal last weekend in which he seemed open to the bill if improvements could be made and discussed meeting with Rubio to make them.

“He’s done a great job selling this to conservative talk show hosts and others in the conservative community,” McCain said.

But Rubio’s moves unsettle liberals who fear that the insistence on establishing new border requirements first could end up making the path to citizenship unachievable.

“I just hope he doesn’t think he can give away the store and count on the kind of unified Democratic support we have now,” said Frank Sharry of America’s Voice, an immigrant advocacy group.

One change Rubio has focused on would give Congress, instead of the Homeland Security Department, a bigger role in creating a border security plan since many Republicans are skeptical of the Obama administration’s commitment to enforcing border security. As he described it on Hewitt’s show Tuesday, the plan would be legislated as part of the immigration bill, although other Republicans, including Sen. Rand Paul, R-Ky., have discussed having Congress vote on whether the border has been secured.

“People don’t want to just turn it over to the Homeland Security Department to come up with a plan,” Rubio said. “They want the plan to be laid out specifically with real measurables, and I think that’s a good approach and so we’re working with members now to do that.”

(AP)