So what do you think the Republican Party would do if this is true? Tell them both they are no longer Republican contenders for the Presidency?
But if it were not billed as a debate, but rather scheduled guests on a radio political talk show and they discussed their visions for America, I don't think the Republican Party could do a thing. Nor do I believe they would do any thing even if it were against the Party rules, and it was billed as a debate. Then again, they are the Stupid Party, thanks to the GOP Establishment. So who knows what the idiots would do.
https://www.gop.com/rnc-approves-debate-rul/
It actually would not be “illegal”, it would just disqualify the two from further sanctioned debates.
Of course, the committee could saction the debate, and problem solved.