Rubio's leading role in the Senate's passage of comprehensive immigration reform legislation in 2013 continues to be black cloud over the otherwise popular junior senator from Florida -- at least when it comes to the Republican primary.

Former Florida Governor Jeb Bush and Wisconsin Governor Scott Walker have backed a path to citizenship for undocumented immigrants. So has Kentucky Senator Rand Paul and New Jersey Governor Chris Christie. Louisiana Governor Bobby Jindal has as well. Even Sen. Ted Cruz of Texas has not ruled out a path to legalization for some undocumented immigrants. And former governors Rick Perry of Texas and Mike Huckabee of Arkansas both backed their states version of the DREAM Act, a measure that gives undocumented youth access to in-state college tuition. (Pennsylvania Sen. Rick Santorum has never said he supports a path to legalization or the DREAM Act.)

The term amnesty is a loaded one with different definitions depending on who is asked. For the most ardent opponents of immigration, including the group Federation for American Immigration Reform, any way someone can come to the U.S. illegally and stay being permitted to stay, even after a long, arduous process, is considered "amnesty." But it can mean any form of giving immigrants an opportunity for staying in the U.S. legally.

Most of the candidates have shifted their position, saying that first the border must be secure before addressing the 11 million undocumented immigrants. - even though the group FAIR believes that the secure border position is a "red herring," noting that the border can never be completely secure and that as long as an incentive is provided for people to come to the U.S., immigrants will come.Immigration is not likely to be the hot button issue that it was in 2012 when it moved Mitt Romney so far to the right that he backed self-deportation. What could diffuse the issue even more is that the candidates have been on the same page - and not on the side of conservatives - at one point in their careers.

Conservatives who prioritize the issue say, however, that where they stand now and how they explain their "evolution" matters. The severity of the sin and subsequent redemption matters.

There's always something to be said about consistency of conviction unless the consistency of conviction is wrong

"It's not just taking a pure stance. It's not like people are never allowed to change their minds," Steve Deace, influential syndicated talk show host based in Iowa, said. "Is that a conversion on the road to Damascus of the road to Des Moines?"

 The issue might not be as prominent it was in 2012 when Mitt Romney moved so far to the right he backed self-deportation, but the issue will still play a factor for some conservatives.

While Republicans hopefuls have not always espoused the correct position for their party every time, for many conservatives Rubio and Bush have done the most damage on the issue. They say Bush's position is problematic. While he has walked away from a path to citizenship, he strongly supports a path to legalization on the campaign trail.

"There's always something to be said about consistency of conviction unless the consistency of conviction is wrong," Bob Vander Plaats, president of The Family Leader, a socially conservative group in Iowa, said.

As for Rubio, a fellow Floridian, Rubio's leadership role and attempt to placate conservatives on the issue in the 2013 Senate debate is not much better.

"It's not just the position he took on the issue, it's the amount of political capital he expended to sell it - to be the face of it," Deace said of Rubio.

While Cruz never ruled out a path to legalization, his current tough talk about securing the border is pleasing to conservatives ears.

Source: NBC News