Fresh off a win in Iowa, 2016 candidate Sen. Ted Cruz is responding to tweets from Iowa’s number-two pick, Donald Trump, with his own tweet suggesting that Trump join Democratic candidate Sen. Bernie Sanders in contesting caucus results.

On Fox News, Cruz said his rival was throwing a “Trumper-tantrum,” and a President Trump would “nuke” the country of Denmark on a whim.

It is no surprise that Donald is throwing yet another temper tantrum–or, if you like, yet another Trumper tantrum. It seems his reaction to everything is to throw a fit–to engage in insults. And I understand that Donald finds it very hard to lose–that he finds that very difficult for him. But at the end of the day, the Iowa people spoke. Donald Trump guaranteed victory in Iowa. And then he lost. And he doesn’t like that, and his reaction is that he breaks down–he really has problems. You know, he accused the people of Iowa of being stupid. In fact, he skipped the Iowa debate. … Donald’s insults get more and more hysterical the more upset he gets. And that’s fine; he can do that. I’m not gonna respond in kind. [Question: “Do you think they’re funny?] I think they’re very funny. I think Donald–I wake up every day and laugh at the latest thing Donald has tweeted. Because he’s losing it. Look, we need a Commander-in-Chief, not a Twitterer-in-Chief. We need someone with judgment and the temperament to keep this country safe. I don’t know anyone who would be comfortable with someone who behaves this way having his finger on the button. We’re liable to wake up one morning and Donald, if he were president, would have nuked Denmark. That’s not the temperament of a leader to keep this country safe.

The Cruz response also highlighted a video criticizing Trump’s history with Democrats.

Cruz tweeted:

Bernie is contesting #IA results. Maybe Donald should go back to IA & join the Ds. Bet they'd love #TrumpCare https://t.co/uTdU9Uv9sL — Ted Cruz (@tedcruz) February 3, 2016

Cruz’s tweet came with the hashtag “#TrumpCare” and a link to a campaign-video assaulting Trump on associations with pay to play and associations with Democrats like Presidential candidate Hillary Clinton. The video closes with the words, “America Doesn’t Need a Deal Maker. America Needs a Fighter.”

The single response tweet from Cruz came amidst pictures of campaign trail events and thank-you’s from the GOP presidential contender.

Cruz was responding to tweets from Trump attacking the winner of the Iowa caucuses:

Ted Cruz didn't win Iowa, he stole it. That is why all of the polls were so wrong and why he got far more votes than anticipated. Bad! — Donald J. Trump (@realDonaldTrump) February 3, 2016

The Trump tweets continued:

During primetime of the Iowa Caucus, Cruz put out a release that @RealBenCarson was quitting the race, and to caucus (or vote) for Cruz. — Donald J. Trump (@realDonaldTrump) February 3, 2016

Many people voted for Cruz over Carson because of this Cruz fraud. Also, Cruz sent out a VOTER VIOLATION certificate to thousands of voters. — Donald J. Trump (@realDonaldTrump) February 3, 2016

Trump tweeted one more jab:

Based on the fraud committed by Senator Ted Cruz during the Iowa Caucus, either a new election should take place or Cruz results nullified. — Donald J. Trump (@realDonaldTrump) February 3, 2016

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