Republican presidential candidate Donald Trump is accusing rival Ted Cruz of stealing the Iowa caucuses and is demanding a do-over.

“Based on the fraud committed by Senator Ted Cruz during the Iowa Caucus, either a new election should take place or Cruz results nullified,” Trump tweeted Wednesday.

“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,” he wrote.

The inflammatory accusation marked a reversal for Trump, who on Monday night delivered a concession speech thanking Iowans for his second-place finish and congratulating Cruz. On Tuesday night in New Hampshire, he told reporters he was “very happy with what happened in Iowa.”

But by Wednesday, Trump was laying out a list of accusations. He pointed to a mailer sent by the Cruz campaign headlined “voting violation” and resembling an official notice. The mailer showed recipients their history of voting or not in past caucuses, along with the turnout record of their neighbors, and drew complaints from Iowa’s secretary of state.

Trump also called out Cruz backers for circulating a false rumor Monday night that Ben Carson was dropping out of the race as caucusing was underway.

“Actually, I think I came in first,” Trump told supporters at a rally that drew thousands in Little Rock, Arkansas, Wednesday evening, suggesting the rumors may have given Cruz a winning edge. “Oh that voter fraud!”

Iowa Rep. Steve King, a national co-chairman of Cruz’s campaign, wrote on Twitter Monday evening: “Looks like (Carson) is out. … Skipping NH & SC is the equivalent of suspending. Too bad this information won’t get to all caucus goers.” Carson has called the comments “dirty tricks.”

Cruz spokesman Rick Tyler told CNN on Wednesday that Cruz apologized personally to Carson for the mistake. He said the Cruz team “as a campaign” never alleged Carson was dropping out.

“It may be that some of the surrogates or some of our caucus precinct captains … went too far,” Tyler told CNN. If so, he added, “that was in error, that was wrong.”

Cruz, meanwhile, laughed off the attacks, and questioned Trump’s readiness to be commander-in-chief.

“I wake up every day and laugh at the latest thing Donald has tweeted because he’s losing it. We need a commander-in-chief and not a twitterer-and-chief,” said Cruz, who said his two young daughters are “better behaved than a presidential candidate who responds by insulting everyone every day when he loses.”

“I understand that Donald finds it very hard to lose. That he finds that very difficult for him, “he added. “But at the end of the day the people of Iowa spoke. Donald Trump guaranteed a 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.”

Carson isn’t letting the matter rest either. He addressed what he called “dirty tricks” in a briefing at the National Press Club “in response to deceptive Iowa caucus tactics,” according to a campaign statement ahead of the event.

“It’s clear that there were people who tried to take advantage of a situation,” Carson said Wednesday during the briefing.

Trump’s Twitter reaction to his Iowa showing strayed significantly from his public comments on several morning TV shows Wednesday and at a rally on Tuesday night.

Asked about Cruz at a press conference before the rally, Trump said Cruz had insulted Carson and Iowans but would not say whether he thought the Texas senator had run a dirty campaign.

“I don’t know, I can’t tell you yet,” he said.

But Trump campaign manager Corey Lewandowski was pointed on the matter Wednesday.

“What Senator Cruz did to Ben Carson was a disgrace and an insult to Doctor Carson and the process,” he said. “What Senator Cruz did to the voters of Iowa was also a disgrace in regard to their phony voter violation form. Additionally, they misrepresented Mr. Trump and unfortunately this happens all the time with crooked politicians.”

Asked whether the campaign planned to file a formal complaint, he said: “Wait and see.” Officials from the Iowa Republican Party did not respond immediately to questions about their process for handling complaints like Trump’s.

Some of the billionaire’s supporters said they believed Trump had valid complaints about the Iowa caucuses. Wayne Hogan, the owner of a North Little Rock office furniture store who was wearing a Revolution-era jacket and hat along with a Trump shirt, said he shared the billionaire’s concerns about the caucuses.

“You don’t think there’s ever been any fraud in any elections?” Hogan said as he waited outside Barton Coliseum.

But other said they think Trump should be focusing on the next contests.

“That’s history,” said Mark Keith, superintendent of the Camden Fairview School District, who said he’s undecided on who to support in the primary. “I think he needs to move on.”