In the spirit of always fighting the last war, Republicans are kicking around the idea of imposing strict barriers to entry into the Republican presidential primary field four years from now.

“Let’s make running for the Republican nomination a truly conservative affair,” writes John Noonan, former adviser to Jeb Bush. “You want it? Earn it. Raise $5 million for the RNC in the years before the nomination and only then do you qualify to run.”

This kind of thing may be necessary if the GOP is to avoid another Trumpening, but also woefully insufficient. Noonan’s specific idea would be difficult to implement for some of the reasons he lays out in the article. It also probably wouldn’t have stopped Trump from running this cycle, thanks in large part to the Supreme Court’s decision in McCutcheon two years ago, which made it much easier for rich people to raise money for official party committees.

But let’s imagine a rule that would’ve foreclosed a Trump candidacy altogether was in place as of 2015—for instance, one holding that to run, you must have won elected office as a Republican within the past 12 years.

Maybe Trump would’ve just sat the whole thing out. But he might’ve driven a near-majority of the GOP’s base into a third party. Or, he might’ve made the qualifying candidates compete for his endorsement by establishing politically toxic criterion: mass deportation, commitment to a border fence, other commitments that would’ve Trumpified the winning candidate.