Melania Trump and Heidi Cruz are the latest victims in 2016 presidential campaign mudslinging.

In the run-up to Tuesday's Utah caucuses, an anti-Trump super PAC ran ads that featured a photo of Melania Trump, naked and handcuffed to a briefcase, and urged voters to support Ted Cruz.

"Meet Melania Trump. Your next first lady," was written over the risqué photograph, which had been taken as part of a British GQ photo shoot in 2000 on Trump's private plane, before the model's marriage to the businessman. "Or, you could support Ted Cruz on Tuesday," the ad suggested.

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Trump, in a tweet Tuesday night, slammed "Lyin' Ted Cruz" for the ad and threatened to go after the Texas senator's wife, Heidi Cruz:

Lyin' Ted Cruz just used a picture of Melania from a G.Q. shoot in his ad. Be careful, Lyin' Ted, or I will spill the beans on your wife! — Donald J. Trump (@realDonaldTrump) March 23, 2016

While on the campaign trail for her husband in Wisconsin Wednesday, Heidi Cruz responded to Trump's threats herself, saying she isn't "worried" about the remarks.

"You probably know by now that most of the things Donald Trump says have no basis in reality," she told reporters. "So we are not worried in the least - we're focusing on our campaign and we're going to continue to do that."

Cruz said he had nothing to do with the ad and hit back at Trump late Tuesday:

Pic of your wife not from us. Donald, if you try to attack Heidi, you're more of a coward than I thought. #classless https://t.co/0QpKSnjgnE — Ted Cruz (@tedcruz) March 23, 2016

After Cruz's denial, Trump parlayed another attack at his rival Wednesday:

Lyin' Ted Cruz denied that he had anything to do with the G.Q. model photo post of Melania. That's why we call him Lyin' Ted! — Donald J. Trump (@realDonaldTrump) March 23, 2016

During an interview with CNN on Wednesday, Cruz further bashed Trump's attack on his wife, saying that it "reveals a lot about character."

"It reveals a lot about class -- that Donald's instinct is to try to attack my wife and sully her," he said. "That should be beneath Donald, but the reason he's doing that is he had a very bad night," likely referring to Trump's loss to Cruz in Utah.

Then Cruz added a line straight out of the movies: "If Donald wants to get in a character fight, he's better off sticking with me because Heidi's way out of his league."

That line, as pointed out by the Washington Free Beacon, seemed to be taken directly from Michael Douglas' character in "The American President," who told a rival: "You want a character debate, Bob, you'd better stick with me. 'Cause Sidney Ellen Wade is way out of your league."

It's a line similar to one Cruz used before, in defending his daughters against a Washington Post cartoonist. "Classy," he tweeted in December. "@washingtonpost makes fun of my girls. Stick w/ attacking me--Caroline & Catherine are out of your league."

The Texas senator continued to hit Trump Wednesday afternoon, telling reporters in New York that Trump's statements were "gutter politics."

"Sadly, I wasn't surprised. We have grown to see a pattern with Donald. When he's worried, when he's upset, when he's scared, he begins reacting predictably. He begins screaming, he begins yelling, he begins often cursing and then he tried to attack and bully people and that's his pattern he does over and over again," Cruz said. "Now I will say, even for Donald, he reached a new low. It's one thing to try to attack another candidate, it's another thing to come after my wife."