LAS VEGAS — It took just one question about Marco Rubio's signature legislative achievement, the Senate's Gang of Eight comprehensive immigration reform bill, to expose the tortured divisions inside the Republican field on the question of immigration. Rubio offered a talking-points answer that embraced a position — a path to citizenship — that is anathema to many Republicans, while at the same time sidestepping some key questions about his policy proposals. Then rival Ted Cruz rewrote his own history on the subject, followed by aides explaining that Cruz has now adopted a position — "attrition through enforcement" — that is likely to rekindle old fights in the GOP.

In the end, even an attentive and well-informed voter would have a hard time discerning whether either man was being entirely candid about his views.

The exchange began with this question, from CNN's Dana Bash to Rubio: "You co-authored a bill with Democrats two years ago that allowed a path to citizenship for undocumented immigrants. Do you still support that path to citizenship, which means giving those immigrants rights, like the right to vote?"

Rubio began by claiming an especially deep understanding of the issue, describing his life as an insular world in which everyone in his family, everyone in his wife's family, and all of his neighbors are immigrants. "I see every aspect of this problem," Rubio said.

Rubio ticked off a list of requirements for immigration reform that immediately raised flags for anyone who followed the writing and passage of the Gang of Eight bill. First, Rubio said, the U.S. would have to enact a variety of border security and interior enforcement measures. Then, "after we have done those two things, I think the American people are going to be reasonable with what do you do with someone who has been in this country for 10 or 12 years who hasn't otherwise violated our laws, because if they're a criminal they can't stay."

Republicans have a right to be skeptical about whether the federal government would ever implement Rubio's proposals. Congress has in the past backed off its own requirements for a border fence, and a visa entry-exit system has been passed into law repeatedly but never enacted. Beyond that, Rubio's own legislative record undercuts his claim that if illegal immigrants are criminals, "they can't stay." Rubio's Gang of Eight bill would have allowed illegal immigrants with extensive criminal records to live permanently in the United States; only if they had three misdemeanor convictions handed down on three separate occasions — and in some jurisdictions, misdemeanors include crimes like vehicular manslaughter, drunk driving, and domestic violence — would they have been at risk for removal.

And all the while, Rubio avoided the word "citizenship." After his statement, Bash said, "Senator, you haven't answered the question. You described a very long path but does that path end at citizenship?"

"I am personally open — after all that has happened and after ten years in that probationary status where all they have is a permit, I personally am open to allowing people to apply for a green card," Rubio said. What that means, apparently, is that currently illegal immigrants would be given legal status — "probationary status," in Rubio's words — to stay in the country while security measures are being put in place. And then they would be allowed to apply for a green card, which means they can stay in the United States legally for life, and also become a U.S. citizen.

That's not terribly different from the scheme Rubio wrote into the Gang of Eight. Still, after the debate, Rubio aide Alex Conant said a President Rubio would handle immigration far differently from the Senator Rubio of two years ago. "The provisions in the 2013 bill were the product of compromise and not what we would have done if we'd written the bill on our own," Conant said. When a President Rubio approaches the issue, Conant added, he would "fix our immigration system starting with border security," and the resulting process "would not be the same as what the Senate passed in 2013."

Then it was Cruz's turn. "Senator Cruz, on the campaign trail, Senator Rubio has said that his immigration plan is not that different from yours," said Bash. "Is that true?"

Cruz could have said simply that he opposes a path to citizenship, and he opposed it during the Gang of Eight debate. That's true. Instead, Cruz, supposedly a master of debate, allowed Rubio to change the subject. The question had been about a path to citizenship, but Rubio challenged Cruz, saying, "As far as Ted's record, I'm always puzzled by his attack on this issue. Ted, you support legalizing people who are in this country illegally. Ted Cruz supported a 500-percent increase in the number of H-1 visas, the guest workers that are allowed into this country, and Ted supports doubling the number of green cards."

Subject changed. Cruz tried to one-up Rubio by claiming that he, Cruz, opposes not just a path to citizenship but any legalization of illegal immigrants. "Look, I understand Marco wants to raise confusion," Cruz said. "It is not accurate what he just said that I supported legalization. Indeed, I led the fight against his legalization and amnesty."

Yes, Cruz opposed Rubio's Gang of Eight bill, and he did support increases in H-1 and guest worker visas, as well as an increase in green cards. But Cruz's position on legalization is murkier than he suggested.

A huge problem in the Gang of Eight scheme was that it would have offered virtually immediate legal status to millions of illegal immigrants — before new security measures were in place. Cruz sought to address that by offering an amendment that would impose a three-year waiting period for provisional legal status — a period that would allow security measures to get started before legalization was handed out.

But with that important proviso, Cruz said back in 2013 that he did support legalization. Knowing that, Rubio tried to back Cruz into a corner Tuesday night.

"Does Ted Cruz rule out ever legalizing people that are in this country now?" Rubio asked.

"I have never supported a legalization," Cruz began.

"Would you rule it out?" said Rubio.

"I have never supported legalization," said Cruz, "and I do not intend to support legalization."

Looking at the record, it's clear that Cruz, when he offered the amendment to the Gang of Eight bill that would have created the three-year delay in legalization, spoke approvingly of "allowing, as this legislation does, a legal status for those who are here illegally."

Further, in a phone interview with Cruz on May 28, 2013, I specifically asked whether, despite his opposition to a path to citizenship, and given the three-year delay he called for, "You do buy into this whole legalization idea?"

"Legalization is the predicate of the Gang of Eight bill," Cruz responded. "And in introducing amendments, what I endeavored to do was improve that bill so that it actually fixes the problem." If you want to listen, here is the whole exchange:

Cruz's team has tried to explain away that position by claiming Cruz was offering some sort of poison-pill amendment designed to kill the Gang of Eight bill rather than improve it. Cruz did it himself in a somewhat stammering interview with Fox News' Bret Baier Wednesday evening. But the situation is more complicated than Cruz says. Yes, he knew Democrats would never accept his amendments, but he spoke with apparent feeling about including legalization, if delayed, in the final deal.

On Tuesday night, however, Cruz was in full no-legalization mode. And when some reporters questioned whether his comment "I do not intend to support legalization" was some sort of lawyerly way of leaving the door open to someday doing just that, Cruz sent an aide to tell reporters that he no way, no how supports legalization.

"I'm here tonight, and I want to make this super clear to everybody, so put me on the record on this: Sen. Cruz unequivocally, unequivocally, does not support legalization," national campaign chairman Chad Sweet told the Washington Examiner's David Drucker after the debate. When Drucker asked what Cruz would do with the 11 or 12 million immigrants in the U.S. illegally, Sweet answered, "His plan is attrition through enforcement. He's following the rule of law…If we enforce the law, ultimately there will be attrition through enforcement. And in the end, though, what the senator is trying to do, as well, is save and expand our legal immigration system."

Sweet's words — reminiscent of Mitt Romney's "self-deportation" — will likely send a chill through those Republicans who believe the party must embrace comprehensive reform to remain competitive in presidential elections.

So to conclude the long and complicated story: When the Gang of Eight bill was brought up in Tuesday's debate, the author of the bill overstated, and perhaps even misrepresented, some aspects of the legislation, while the chief critic of the bill backed away from previous statements and took a position he has never taken before. Neither man did himself proud.

Still, as far as immigration is concerned, and when all the factors are considered, it's important to remember this: One senator, Rubio, wrote and voted for the massive 1,197-page immigration reform that is now unacceptable to many Republican voters. The other senator, Cruz, voted against it. When it comes to bottom lines, that counts for something.