"In the past I have supported a broad approach to immigration reform - increased border security coupled with a temporary worker program. I no longer do," Flake wrote on his campaign website in March 2011. "I've been down that road, and it is a dead end. The political realities in Washington are such that a comprehensive solution is not possible, or even desirable given the current leadership. Border security must be addressed before other reforms are tackled."
During his 2012 campaign, Flake reaffirmed his support for comprehensive immigration reform, saying that he would pick up such legislation if the border was adequately secured.
Like McCain, Flake's focus on border security leaves him room to negotiate with Democrats. A reform package that includes increased spending on border security in his state could be a potential trade-off.
4. Rep. Luis Gutiérrez (D-Ill.)
The Illinois Congressman has been a highly visible face in the fight for immigration reform. He serves as the chair for the Congressional Hispanic Caucus Immigration Task Force, and rights groups have called him a "champion of immigration reform" for his unwavering support. In 2009, Gutiérrez introduced an immigration reform bill in the House but the legislation never gained adequate support.
He was arrested outside the White House while protesting deportations in August 2011, but backed the Obama candidacy after the administration loosened deportation guidelines for "low priority" immigration cases shortly thereafter.
Gutiérrez and the Hispanic Caucus will be leaders on the issue again, according to Noorani.
"They were so key in terms of pressuring the administration and holding the Democratic Party accountable," he said. "When you talk to folks in the Latino community, Gutiérrez is their leader."
5. President Barack Obama
No single politician will be more instrumental in passing an immigration reform bill than the man in the Oval Office. Not only will he have to secure enough votes in the House and Senate, he'll need to make the case to the American public that reform is needed and possible.
"He definitely came short in terms of demonstrating leadership on the issue," said Cristina Jiménez, managing director of United We Dream. She compared passing immigration reform to healthcare: "He's going to have to do whatever it takes."
Four years ago, the political discussions about immigration reform largely took place behind closed doors, as the president spent his time trying to sell people on sweeping healthcare legislation. Legislation by Gutiérrez didn't gain traction in the House nor did a bill by Sen. Robert Menendez, D-N.J., in the Senate.
According to Frank Sharry, the strategy should change this time around.
"It would be wise for the president to spend more time on the road talking about this issue than in the back room negotiating," he said. "The right strategy is to have a very public discussion on immigration policy and immigration politics."