West Des Moines, Iowa CNN  — 

Ted Cruz and his allies hoped to escalate their attempted game of chicken on Wednesday night, offering Trump a $1.5 million prize and extending him a formal invitation to come debate Cruz one-on-one in the final nights before the Iowa caucuses.

Two of the biggest megadonors behind Cruz’s presidential ambitions offered personal donations to Trump’s favorite veterans’ charities if the businessman agreed to face the Texas senator. The dare comes on the eve of the next Republican debate in Des Moines, Iowa, which Trump has pledged to not attend.

The Trump campaign did not immediately respond to a request for comment.

Cruz has criticized Trump since he said he was skipping Thursday’s debate.

On Wednesday evening, Cruz got specific with the debate challenge he extended a day earlier, inviting him to match in a “Mano-a-Mano” event this Saturday at Western Iowa Tech University in Sioux City at 8 p.m.

“We have a venue. We have a time. All we’re missing is a candidate,” Cruz told a ballroom crowd. “It’s not that he’s afraid of me. He’s afraid of you. He doesn’t want to answer questions from the men and women of Iowa about how his record doesn’t match what he’s selling.”

Immediately after Cruz finished his remarks, his campaign wrote Trump a formal invitation, saying it “anxiously awaits” Trump’s reply.

Cruz appeared more willing than ever to needle Trump from the stage, saying that Trump had not been in the fray during the seven big conservative fights of the past three years. And Cruz repeated belittled Trump as a “fragile soul.”

“You know, I said everyone would say they oppose Obamacare, but there’s actually one candidate on that stage – well, actually technically speaking now not on that stage – who doesn’t say that,” Cruz said. “Donald is entitled to have that view. You might even call that view a New York value. You know, as Donald might observe, both he and Bernie Sanders are native New Yorkers.”

Cruz christened Trump’s health care plan as “Trumpcare,” saying it is effectively no different from the plan of Democratic candidate Bernie Sanders.

Trump has said he won’t participate in Fox News’ debate on Thursday because of alleged bias of one of the moderators, Megyn Kelly. But the latest pitch for a face-off with Cruz came not from the candidate himself, but from the families of Toby Neugebauer and Robert Mercer, who together have invested $21 million in super PACs supporting Cruz.

“Senator Cruz and Mr. Trump both respect the veterans and hold them in the highest regard but Senator Cruz respects the process and we are calling on Mr. Trump to do the same and debates are the purest form of democracy,” the donors said in a statement. “Iowans – and Americans – deserve to hear from the front-runners in this ‘two-man race’ one last time.”

The gift to the veterans’ organizations would only come if the two debated on or before this Sunday in Iowa; if it only featured Trump and Cruz; if the moderator was picked by the candidates; and if the event lasted for one hour, the super PACs, together called Keep the Promise, said.