Apparently nervous about a primary challenge from an anti-immigration Tea Party candidate eyeing his job, McCain's sudden hard line represented a dramatic turnaround from the Arizona senator's record in Congress, where he championed unsuccessful immigration reform bills in 2007.
What a difference a presidential election makes — one in which the overwhelming majority of Hispanics, the country's fastest growing voting bloc, cast their ballots for Barack Obama, despite the president's own inaction on immigration reform.
McCain is serving once again as one of the Republicans' most vocal proponents for a sweeping immigration overhaul. He was one of the key architects of a bipartisan deal reached in the U.S. Senate this week that calls for a path to citizenship for millions of the country's illegal immigrants.
Hours before Obama unveiled details of his own immigration proposals in Nevada, McCain was front and centre on the morning talk-show circuit, emphasizing the urgent need to address the issue.
"We cannot have, forever, 11 million people living in the shadows in this country," said the former presidential candidate, dubbed the "Republican weather vane on immigration" by the Washington Post.
This time around, however, McCain seems as motivated by politics as he is by compassion, reminding his fellow Republicans repeatedly that they face political extinction if they don't get on board.
"When a Democratic candidate gets 71 per cent of the vote, you can do the math and see the (party's) descent towards irrelevancy or failure to win an election," McCain said on MSNBC.
Earlier this week, he went further.
"If we continue to polarize the Latino slash Hispanic vote ... our chances for being in the majority are minimal," he told CNN.
"Many of us believe that they are a natural constituency of ours; small business, less regulation, big service in the military, pro-life, all of those reasons. But this issue of illegal immigration has obviously been a major driving factor in the decision-making of the Hispanic voter."
The proposed Senate deal announced Monday — reportedly pushed forward with haste by Republican senators, who wanted to beat Obama to the punch — includes strong border security measures that would kick in immediately if signed into law.
That doesn't necessarily include a proposed fence along the U.S.-Mexico border, something McCain opposed in 2007 before calling for its completion in a 2010 campaign ad.
The longtime senator has suggested the prerequisite border security measures in the deal are aimed at winning over the more conservative lawmakers in the U.S. House of Representatives.
"We will and already are reaching across the capital," McCain said. "I think Republicans realize the realities of the 21st century."
If so, those Republicans are apparently perceived as being in need of some basic schooling as they come to grips with those realities.
A memo sent to congressional Republicans this week by a conservative Hispanic advocacy group co-chaired by Jeb Bush had some no-brainer tips on immigration reform talking points.
"Don't use phrases like, 'Send them all back,' 'electric fence,' 'build a wall along the entire border,'" read the memo from the Hispanic Leadership Network, obtained by various news outlets.
Obama urged Americans to remember their history amid the immigration reform debate as he addressed a Las Vegas high school.
"It's easy for the discussion to take on an air of us versus them," he said. "We forget that most of us used be them."
He also praised the Senate deal, but urged lawmakers to move fast to pass it.
"If Congress is unable to move forward in a timely fashion, I will send them a bill based on my proposal and insist they vote on it," he said.
Obama's proposals differ in two ways from those of the Senate.
They would treat same-sex, bi-national couples the same way as they would straight couples. And they wouldn't require illegal immigrants to wait to seek full citizenship until border security has been beefed up and a new system has been implemented to keep tabs on the employment status of migrant workers.
The president is reportedly concerned such measures could result in in illegal immigrants waiting years for citizenship.
Those differences could serve as serious stumbling blocks with congressional Republicans in the weeks ahead.
"Unless there's real enforcement triggers, we're not going to have a bill that moves on," Republican Sen. Marco Rubio warned Tuesday in an interview with conservative radio host Rush Limbaugh.
McCain, meantime, took aim at the same-sex component of Obama's proposals — measures that will clearly not be warmly embraced by conservatives in the House.
"That to me is a red flag that frankly we will address in time," McCain said, adding he didn't think the issue was of "paramount importance at this time."
A gay Republican group criticized McCain for those remarks.
"It defies logic that Sen. McCain would craft an immigration proposal that would reward gay people who came to this country illegally with a path to citizenship, but deny legal gay couples the opportunity to access the same immigration rights as opposite-sex couples," GOProud's Jimmy LaSalvia said in a statement.