[Fhios]

Probably be struck down by the courts as changing election rules during an election is generally frowned upon.

Now, whether the courts take it up in a speedy and judicious manner, that’s a new question.

[Nep Nep]

It’s not “changing the rules during an election”. The campaigns may have started but the changing of rules prior to an election is routine, happens all the time both within party structures and legislatively. The wisdom of particular moves aside, changing rules ahead of time is perfectly normal and legitimate.

[Aliska]

Maybe ex post facto would apply. The rules would constitute the force of law. Trump declared June 16, 2015. Many others declared before that. A couple declared after that but in time to make the debates.

They want to change the rules after-the-fact. I don't know if there are any legal precedents but I'm sure they can't keep moving the goalpost.