But on the campaign trail, Rubio says he's open to the most controversial aspect of that plan: a pathway to citizenship for the nation's 11 million undocumented immigrants. Rubio laid out this week a list of criteria illegal immigrants would have to meet to earn citizenship -- mirroring the controversial Gang of Eight bill that he has methodically been distancing himself from after it passed the Senate in 2013.
The comments drew Rubio back into the fray of an issue that has dogged him with the right wing of the party since he first tried to tackle it in 2012. He has tried to project himself as a leader trying to fix a vexing issue, while also trying to be sensitive to the anger from the GOP base.
But by playing to both sides, Rubio has sparked criticism from the left and right and prompted sharp charges that he's choosing his position for political expediency. It's a sign that the issue is only going to heat up as he continues to ascend in the GOP race.
Sen. Jeff Sessions, R-Alabama, an immigration hardliner and an aggressive opponent of the 2013 bill, told CNN on Thursday that GOP candidates should drop out of the race if they back a path to citizenship.
"Supporting citizenship for illegal immigrants should be disqualifying," Sessions said when asked about Rubio's position. "Just like we can't have a GOP nominee who supports Obamacare, we can't have a GOP nominee who supports amnesty."
Alabama Rep. Mo Brooks said in an interview that Rubio's position on immigration would "very significantly" depress conservative voter turnout in a general election if he were the nominee.
"When I see what Marco has said and done, along with other presidential candidates, that is: Their actions and their comments are a definite concern because they undermine the ability of American families to earn enough to take care of themselves," said Brooks, a conservative Republican who backs Texas Sen. Ted Cruz for the nomination.
On Thursday, Rubio tried to muddy the waters even further by telling reporters that Cruz was aligned with his position on immigration reform, citing positions on H-1B visas and other matters that the Texan took during the 2013 battle.
"I don't think our positions are dramatically different," Rubio said
But Rubio spokesman Alex Conant said the Florida senator has made clear he now opposes moving on a bill in a comprehensive fashion, saying Washington must enact individual pieces of immigration reform -- starting with border and interior enforcement -- before debating a path to citizenship.
"What he has said is that the Gang of Eight bill is dead, and it's not coming back and it has even less support now than it did two years ago," Conant said Thursday. "It's clear that the only way that the way to fix the broken immigration system is by first securing the border."
Rubio's immigration past
In April 2012, a 41-year-old Rubio called a small group of reporters into his conference room to announce a rather bold step: He wanted to offer some children of undocumented immigrants the opportunity to apply for "non-immigrant" visas before they would be allowed to earn a more permanent legal status.
The plan stopped short of offering a full-blown path to citizenship, as Democrats wanted. But it elevated his stature and showcased his willingness to dive in the choppy immigration waters -- just as the GOP's presidential candidate, Mitt Romney, had veered right on the issue and was considering picking him as the party's vice presidential nominee.
But in June 2012, Rubio gave up on that plan. President Barack Obama, in an election-year move, took executive action to defer deportations to certain undocumented immigrants brought to the country as children. Rubio said such executive actions undermined an effort to do anything legislatively.
"People are going to say to me, 'Why are we going to need to do anything on this now. It has been dealt with. We can wait until after the election,'" Rubio told the Wall Street Journal
at the time. "And it is going to be hard to argue against that."
After Romney was routed with Hispanic voters in the 2012 elections, a bipartisan group of senators began negotiating behind the scenes to put together a sweeping proposal that they intended to push through Congress in 2013, when Democrats controlled the Senate and occupied the White House.
For months, Rubio was flirting with the group and privately negotiating details, but hadn't made a formal decision about signing onto the legislative proposal until April 2013, when he went on all the Sunday talk shows to aggressively defend the effort.
"This is not blanket amnesty," Rubio said at the time.
As the measure headed to the Senate floor, Rubio sided with fellow negotiators to defeat any controversial amendments aimed at changing the structure of the plan. He voted against an amendment by Sen. John Thune, R-South Dakota, to require the completion of 700 miles of
fencing at the border before allowing the pathway to citizenship plan to move forward. And he opposed a plan by Sen. David Vitter, R-Louisiana, requiring that the country's biometric entry-exit system of tracking people crossing the border is fully implemented before giving legal status to undocumented immigrants.
Moments before the bill's passage, Rubio, the son of Cuban immigrants, said: "Generations of unfulfilled dreams will finally come to pass," adding: "That's why I support this reform."
People 'are going to have to be deported'
But after the bill's passage, Rubio began to speak much less frequently about the matter. Even though the rest of the Gang of Eight was still meeting regularly to strategize over how to ratchet up pressure on House Republicans to take up the bill, Rubio refused to do so, saying that the issue was now in the hands of the GOP-led House, which never called the plan up for a vote.
By taking that approach, Rubio began to make amends with many conservatives who were furious at his position, but he angered fellow proponents of immigration reform who believed he was caving to political pressure.
In an interview with CNN last week
, Sen. Chuck Schumer, D-N.Y., one of the co-authors of the bill, said Rubio was initially "totally committed" to the Gang of Eight plan and that his fingerprints were "all over" the creation of a pathway to citizenship.
"The fact that he abandoned the bill so quickly because a bunch of right-wing commentators came out against it will not serve him well in his presidential campaign primary or general if he ever got there," Schumer said.
By 2014, Rubio began to blame the president for scuttling immigration reform, saying voters had lost trust with him on enforcing existing law since Obama has acted, in his opinion, illegally by the executive actions he's taken. The crisis at the Southern border, where scores of undocumented children were trying to enter the country last summer, made it even harder politically for Rubio to defend the bill. And he has increasingly said that doing anything legislatively in such a major fashion would be a mistake.
"Every massive piece of legislation that has passed over the last 20 years has by and large been disastrous," Rubio told Politico
In recent days, Rubio's immigration position has begun to come into sharp focus, even though he was spared from the back-and-forth during the GOP presidential debate in Milwaukee earlier this week.
Despite being an early proponent to give relief to children who arrived in the country illegally at a young age, Rubio has made clear that the president's deferred action program must "end." He
cosponsored a bill last month to crack down on sanctuary cities.
Rubio has dismissed Donald Trump's call to round up and deport the 11 million illegal immigrants as not "reasonable," but he added that some undocumented immigrants would be deported.
"There are going to be people who are going to have to be deported," Rubio said in Hilton Head, South Carolina on Thursday. "Criminals will be deported. People who have not been here long enough will be deported. We will enforce our immigration laws."
Yet, Rubio has signaled an openness to eventually let the 11 million undocumented apply for citizenship, after paying back taxes and fines and taking other punitive steps -- echoing the call in the Gang of Eight plan that would have created a 13-year pathway to citizenship. But that would only happen, he said, after separate individual pieces of immigration reform are enacted, including border security and fixing the existing legal immigration system.
Some on the right are still not satisfied.
"Republican voters are tired of leaders who promote an immigration agenda that serves everyone's interests but theirs," Sessions said.