NASHUA, N.H. — 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.

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.

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.