(CNN)Ten years ago, Sen. John McCain fell fast and hard from his perch as the overwhelming frontrunner for the Republican presidential nomination.
Trump tasks GOP with solving immigration, the issue that divides it most
It happened for one reason: He supported comprehensive immigration reform.
The Arizona senator not only backed a path to citizenship for undocumented immigrants in 2007, but also helped write an ill-fated bipartisan Senate bill.
I was covering McCain's presidential campaign at the time, and remember his political aides warning him that supporting what powerful GOP primary voters regarded as amnesty would likely hurt him. That was an understatement.
McCain dropped so low that in some polls he was an asterisk -- the symbol that appears when support is too small to even measure.
He climbed back up to eventually become the 2008 GOP nominee because of his grit and determination, and also because he abandoned any talk of citizenship for undocumented immigrants.
I remember attending more than one McCain town hall, from New Hampshire to South Carolina, where he got an earful from angry Republican voters as he tried to convince them that he learned his lesson: Border security is what they want.
That was a decade ago, but today immigration is still splitting the GOP just as much -- which will become more evident in the next several months, as the Republican-controlled Congress grapples with how to deal with an estimated population of 800,000 immigrants whose future in the US is now uncertain.
DACA dividing lines
This week, as we saw protests about President Donald Trump's decision to end the Deferred Action for Childhood Arrivals (DACA) program, which gave legal status to undocumented immigrants brought to America by their parents, Trump called on Congress to act.
And on the right -- among core conservatives who helped elect Trump -- the outrage is aimed at the President asking Congress to write legislation giving what they consider amnesty to undocumented immigrants.
"I'm hopeful the base will rise up," Rep. Steve King, R-Iowa, told my CNN colleague Kate Bolduan this week.
He and others argue the President should have just ended DACA -- without the six-month window for Congress to act -- as he promised during the 2016 campaign. The reason he didn't, they say, is because many of the conservatives who helped get Trump elected, like former White House chief strategist Steve Bannon, are no longer in the West Wing.
"The voices of those who would be more open-borders, pro-amnesty advocates -- seem to be prevailing," King added.
Bannon may no longer be able to walk down the hall to talk to the President, but he is back at the helm of Breitbart, where he is already working to gin up like-minded conservatives on immigration.
"I don't agree with that DACA decision," Bannon said on CBS News this week.
"Trust me, the guys on the far right, the guys on the conservative side, are not happy with this," Bannon added.
But Republican leaders may not need votes from those conservatives. They very well could find bipartisan agreement with Democrats to give legal status to those protected by DACA, frequently referred to as Dreamers, and couple it with border security, and pass it over objections of many on the right.
It would be exactly what polls show the vast majority of voters want: Allowing Dreamers to stay in the US.
A Pew Research poll from earlier this year found 72% want people who came to the US illegally as children to remain and apply for legal status. Just 26% disagree with that, but inside the GOP even a small percentage can be vocal and powerful.
That's why when it comes to Republican party politics, legislation allowing DACA recipients to stay in America legally would split the GOP wide open again, and leave some GOP lawmakers who vote for it open to primary challenges from those who call it amnesty.
And those primary challengers would be encouraged through sites like Breitbart and other conservative outlets.
Republicans tried in 2012
After another GOP presidential loss in 2012, the Republican National Committee performed what it called an autopsy on the defeat. One of the key takeaways was that Republicans must repair their relationship with Latino voters, only 27% of whom went for Mitt Romney in that election. The recommendation was for Republicans to pass comprehensive immigration reform in the hopes that Latino voters would be more open to Republican candidates.
In 2013, Republicans returned to Congress and tried to do just that.
One of the architects of that bill was Sen. Marco Rubio, R-Florida, who was already strongly considering a 2016 run for president.
Rubio and his political advisers were fully aware of McCain's cautionary tale -- almost losing the GOP presidential nomination because of his fight for immigration reform.
But just like McCain before him, Rubio decided to do what he thought was right, despite the political minefield inside the GOP.
I remember asking Rubio about it on more than one occasion in the Capitol hallways, and he made clear he knew his stance was controversial.
"I understand why conservatives are upset. They've seen all these promises in the past that haven't been delivered. That's why we're saying that nobody can become a legal permanent resident of the United States unless these border measures pass," Rubio told me in June of 2013.
Unlike the 2007 effort, the 2013 bill actually passed the US Senate later that month with broad bipartisan support and a vote of 68 to 32.
But in the GOP-led House, conservatives revolted and House Speaker John Boehner -- a proponent of immigration reform -- never brought it to the floor for a vote.
2016 was set to be different for the GOP, but then came Trump
As the 2016 GOP presidential primary race began several candidates -- especially early frontrunner, former Florida Gov. Jeb Bush -- were for immigration reform. And though he answered questions about it when asked and didn't run from it, other candidates who supported a path to citizenship for undocumented immigrants -- like Rubio -- tried to steer clear of the divisive topic.
That became virtually impossible on June 16, 2015, when Trump entered the race. He said throughout the primary season that he was the reason immigration was a hot topic, that no one was talking about it before he jumped in with an instantly infamous announcement speech.
"When Mexico sends its people, they're not sending their best. They're not sending you. They're not sending you. They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people," Trump said.
And though Trump, as a candidate and later as President, promised to treat Dreamers with humanity, apparently torn about the issue, many in his base are not.
Now, by having Congress deal with the issue, politically it means that in the short term, every House Republican on the ballot in 2018 is now on the hook.
2017 McCain: GOP wants 'to get the issue behind us'
I caught up with McCain this week in the Capitol -- the man who learned the first modern lesson on the perils of trying to appeal to GOP primary voters while supporting anything they may view as amnesty.
And yet, he has come full-circle. He wants to tackle comprehensive immigration reform again.
"My advice is that we go back to what got 68 votes in the United States Senate, and that was comprehensive. For example, we had the guest worker programs, we had e-verify, we had provisions for enforcing the border," McCain said.
"We were going to have to take up this issue at some point or another," he added.
"I think most members would like to get the issue behind us," McCain insisted.
That didn't work in either 2013, with Democratic President Barack Obama, or 2007, with Republican George W. Bush in the White House.
The X-factor now is Donald Trump.
Republicans in pro-reform circles hope he can pull a "Nixon in China" move on on the issue -- a political metaphor for an out-of-character act by a politician, in this case, immigration hardliner Trump turning around and backing comprehensive reform.
The conservatives who got him elected are determined to make sure that never happens, and worry that immigration -- the issue that consistently splits the GOP -- is about to crack it open once again.