Can the GOP ban Trump from running again? Should they?

They can vote to IMPEACH and remove him, and  THAT would prevent a future run. 

Or they can remove him thru the 25th amendment, and that would  *probably*  sink any further hopes......(but maybe not!) 

But after he's dragged out of the white house.........Trump will spiral quickly into sheer insanity....... and then all his lawsuits will start, and he will just declare  diminished mental capacity to stand trial. 

That might even be his plan. 

If they impeach and convict him for sedition, yes.

People would not let  you to do this to Trump.

There was an attempt to keep Bernie out based on the belief he wasn't a Democrat. I suppose he could be expelled from the GOP. If they have a similar rule it would keep him off the ballots.

You mean would they? They love this freaking guy.

The American people or at least those with some sense already banned him.

*Sigh*.......Move to Russia if you want an autocracy