Something remarkable happened Tuesday night in Las Vegas, according to Ted Cruz: His Republican rival for the White House, Marco Rubio, finally copped to his biggest political vulnerability in front of 18 million Americans — his central role in immigration reform efforts two years ago that have since become toxic to the GOP base.

To hear Cruz tell it, the moment was a turning point, one that would finally bring Rubio's support for a path to citizenship to the fore in a way it has not been highlighted before. Yet in the three days following the debate, it was Cruz who found himself contending more than Rubio with his involvement in the so-called "Gang of Eight" bill, a development that has put the Texan in his most defensive posture since entering the race.

Cruz's campaign forcefully sought to change that Friday. In a decisively more offensive stance toward Rubio, Cruz's aides zeroed in on the Floridian's absence from a high-profile vote in the Senate and sharpened their questioning of whether he was betraying Sunshine State voters when he joined the Gang of Eight. And as the day wound down Friday, the campaign unleashed its closest thing yet to an attack ad, altering a previously released spot on Cruz's Gang of Eight opposition to include an image of a jubilant Rubio flanked by Democratic colleagues who also worked on the bill.

In a news release late Friday deeming Rubio "Too-Cute (By Half) Marco," the Cruz campaign flagged a promise Rubio made while running for Senate in 2010 to "never support any effort to grant blanket legalization amnesty to folks who have entered or stayed in this country illegally." Earlier in the day, Cruz's campaign dispatched one of its highest-profile surrogates in Iowa — evangelical leader Bob Vander Plaats — to try to put Rubio in his place.

"It's fair to have policy differences within the Party, and I think it's helpful to have that debate. What we shouldn't do is intentionally mislead Americans about the positions of others — and it's disappointing Senator Rubio has chosen that path," Vander Plaats said in a statement. "Perhaps even more disappointing is that Senator Rubio explicitly ran against amnesty to get elected in 2010. I think that deeply hurts his credibility with Iowans as they evaluate who they can trust as president to do what he said he would do."

Cruz's campaign is convinced that any minute spent debating immigration with Rubio is a net positive for the Texas senator. That's because history tells a straightforward tale, according to Cruz's campaign: Cruz led the fight against the Gang of Eight bill, while Rubio's fingerprints are all over it.

"Now that's all we're talking about," Cruz spokesman Rick Tyler said Friday on Bloomberg TV. "I don’t know why they think they would benefit from that, but I’m happy to talk about immigration all day long because my guy’s solid on immigration, and their guy has a fatal flaw if you’re running for the Republican nomination."

Rubio's campaign appears willing to let immigration be the topic of conversation in pursuit of a broader narrative that undercuts Cruz's claim to being the only "consistent conservative" in the GOP field.

"When you spend your whole time telling people that you’re a clear talker and you say what you mean and everyone else is a sellout, but you’re the only purist, I think it’s fair to say, ‘Well, hold on a second. Here’s where you’ve been in the past on some issues and here’s where you are now,’" Rubio said in an interview set to air Sunday on CBS' "Face the Nation."

Central to the Cruz campaign's new offensive Friday was Rubio's Senate attendance record, which has already fallen in the crosshairs of GOP opponents such as former Florida Gov. Jeb Bush. Rubio skipped a key vote Friday morning on a $1.1 trillion omnibus spending bill, legislation that both he and Cruz oppose but on which only Cruz showed up to vote no.

Cruz aides, some using the hash tag "#MarcoNoShow," pounced on Rubio's absence from the vote — he was stumping in Iowa at the time — also needling him over his relatively slow schedule on the campaign trail.

".@marcorubio FOUND! - Missed the spending bill vote today b/c he had 1 event in a row in Iowa - a record-setting breakneck pace for Marco," Tyler tweeted.

Yet Cruz stopped short of amplifying his staff's zealousness throughout the day, first in a gaggle with reporters Friday afternoon in Virginia then in a TV interview that aired Friday evening. Asked how he thought Rubio would have voted on the bill, Cruz told Fox News host Greta Van Susteren he did not know.

"I am not my brother's keeper," Cruz added with a smirk. "He was not in the Senate, and so I imagine he was somewhere or doing something else other than standing up against the Washington cartel here in the Senate."

Asked why Rubio skipped the vote, campaign spokesman Alex Conant said in a statement that the bill is an example of the kind of backroom dealmaking the Floridian is running for president to change. In an interview Friday with CBS, Rubio defended his decision to skip the vote, using an explanation similar to what Cruz said after missing the confirmation vote for Attorney General Loretta Lynch earlier this year. "In essence, not voting for it, is a vote against it," Rubio told CBS.

Yet even as the Cruz campaign found its footing Friday against Rubio, questions continued to crop up about the Texan's immigration views. During campaign stops in Virginia and Georgia, Cruz was asked again and again how exactly he planned to deal with the 12 million people already in the country illegally.

"My position is very simple," Cruz told reporters before a rally in Atlanta. "I oppose amnesty. I oppose citizenship. I oppose legalization ... today, tomorrow, forever." He repeated the mantra in response to a similar question minutes later, adding: "Period. The end."

The questions did not stop there. In an interview Friday morning with conservative radio host Laura Ingraham, Cruz said his campaign chairman, Chad Sweet, was "wrong" when he told reporters after the debate that Cruz ultimately wants to "expand our legal immigration system." Sweet reportedly made the same promise during a closed-door meeting Monday with a group of Latino Republicans.

Then, as Cruz was flying between Virginia and Georgia on Friday, The New York Times published a story detailing a memo Cruz wrote to George W. Bush while working on his 2000 presidential campaign. The five-page document "advocated a far more equivocal answer to the question of what to do with those in the country illegally," the newspaper reported, quoting Tyler as saying, "Cruz captured his boss's position perfectly."

Cruz did little to put the issue to bed in an interview on Fox News that aired Friday night. The interview with Van Susteren was Cruz's testiest in recent memory, featuring the two squabbling for several minutes over the true intent of his Gang of Eight amendment and other immigration issues. "What don't you understand, Greta?" Cruz said at one point, visibly irritated.

To be sure, the Cruz campaign has had ample good news to take comfort in since the Las Vegas debate. It has won the endorsements of two influential figures in conservative circles, Ken Cuccinelli and James Dobson, with more high-profile endorsements expected in the coming weeks. Cruz has seen his top-tier status confirmed by at least one post-debate poll that showed him in second place nationally, albeit far behind Trump. And Cruz has drawn large, enthusiastic crowds while crisscrossing the country for a weeklong tour of nine, mostly southern states.

It is in some of those deeply conservative states that the immigration debate is most pitched. Cruz is set to hold rallies Saturday and Sunday in Alabama, the home of perhaps the most hardline opponent of illegal immigration in the U.S. Senate, Jeff Sessions. In an interview Friday, another member of Congress from the state suggested its GOP primary voters see a clear divide in the field when it comes to immigration.

"Rubio would be strong if not for his support of amnesty and open borders," said U.S. Rep. Mo Brooks, who has endorsed Cruz. "That just about kills Marco Rubio in Alabama."