Jeb Bush, Marco Rubio Navigate 2016 Politics with Immigration Debate

Conservatives begin to turn on Rubio's immigration reform efforts.

Protestors rally at Rubio's office against the immigration reform bill.

Protestors rally at Rubio's office against the immigration reform bill.

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With immigration reform the pre-eminent issue currently facing the Republican Party, two potential 2016 presidential candidates are doing what they can to navigate the shark-infested waters and strike a balance between widening their appeal without alienating their base.

[READ: Immigration Bill Finally Heads to Senate Floor]

National Republican leaders have cited a failure to win Hispanic voters as one of the major issues facing the party's ability to win the presidency.

Former Florida Gov. Jeb Bush said Thursday conservatives who oppose supporting comprehensive immigration reform have a right to on principle, but he sees it as an opportunity.

"I don't view immigration as a problem, I view it as embracing an enormous opportunity for us to fulfill our potential as a nation," he said during a forum hosted by the Bipartisan Policy Center. "We'll be overwhelmed by our problems if we don't grow economically. And there are other elements of an economic growth strategy, but without immigration I don't see how we can do it."

Bush, who recently authored a book on immigration reform, found himself floundering in March when he appeared to flip-flop on supporting a path to citizenship for immigrants already in the United States. He appeared more confident Thursday, dismissing critics as lacking substantive policy understanding.

[ALSO: Why Marco Rubio Has to Have It Both Ways on Immigration Reform]

"Our democracy doesn't work when we are just chirping on the sidelines, it works when people are engaged in good faith and try to find consensus," Bush said. "We're living in a hyper-partisan, hyper-political world. The book we wrote … has a set of recommendations that are eerily similar to what's being discussed in the Senate and in the House, so I feel pretty good about that."

But while the immigration reform bill continues to march through the legislative process, the heat is beginning to turn up on key author Sen. Marco Rubio, R-Fla., one of eight senators who worked in a bipartisan group to craft it.

Rubio, whose parents emigrated from Cuba, has been ubiquitous in conservative media outlets throughout the process, taking the lead in selling the measure to his party. At first, conservative thought leaders – such as Rush Limbaugh – expressed a willingness to trust Rubio and remain open to potential reforms. But as the legislative details have emerged, many Republicans have pushed back, saying it's too lenient on border security and that it incentivizes or rewards illegal immigration. And some are taking sharp aim at Rubio, who like Bush, is rumored to have 2016 presidential ambitions.

[BROWSE: Political Cartoons on Immigration Reform]

"Either Marco Rubio is being played the fool or we are being played the fool by Sen. Rubio," wrote Erick Erickson, a conservative blogger at Thursday. "He has become the face of support for this legislation and much of the support of the legislation from those on the right has come because of the good will so many of us have for Sen. Rubio."

Ann Coulter, another top conservative pundit, also jumped on Rubio's leadership, even proposing he face a conservative primary opponent.

"Democrats terrify Hispanics into thinking they'll be lynched if they vote for Republicans, and then turn around and taunt Republicans for not winning a majority of the Hispanic vote," she wrote on her blog Wednesday. "This line of attack has real resonance with our stupidest Republicans. (Proposed Republican primary targets: Sens. Kelly Ayotte, Jeff Flake, Lindsey Graham and Marco Rubio.)"

Rubio has also received criticism from both sides of the aisle for seeming to waver on whether or not he will vote in support of the very measure he helped draft, stating recently that unless border security provisions were strengthened he would not.

[READ: Both Parties Lukewarm on Immigration Reform Package]

"If we have an immigration reform bill that secures the borders, ensures that we don't have another wave of illegal immigration in the future and protects the American taxpayer by denying federal benefits to those who have violated our immigration laws, we will have immigration reform," he recently said on Fox News. "If we fail to do that, if the Democrats or whoever refuses to agree to that we will not. It hinges on that."