Will Republicans hang a “Members Only” sign on their primaries in 2020? Conservatives and party leaders have begun approaching a consensus on one particular reform to the primary process, Politico’s Kyle Cheney reports, that both believe could have prevented the rise of Donald Trump. They want to convince state parties to end eligibility for non-Republicans to vote in primaries and caucuses, although getting states to follow through might be problematic:

Conservatives, still reeling over the looming nomination of Donald Trump, are pushing new Republican primary rules that might have prevented the mogul’s victory in the first place: shutting out independents and Democrats from helping to pick the GOP nominee.

Trump romped in “open primaries” where non-Republicans voted by the thousands and may have influenced the outcome — especially in early states that set the tone of the entire race. Trump’s most successful rival, Ted Cruz, thrived in states with closed primaries where only Republicans were permitted to participate.

Now, Cruz’s allies — hundreds of supportive convention delegates that he helped elect — hope to use the national convention in Cleveland to shove states toward closing their open primaries. And if they’re successful, it will not only go a long way toward warding off a Trump-like candidacy, it will tilt the primary toward conservative candidates in 2020 and beyond.

The advocates are finding a sympathetic ear at the very top of the party. Republican National Committee Chairman Reince Priebus has long supported closed primaries, but has never had a constituency to back him on it. “I believe that only Republicans should vote in Republican primaries,” he said Friday at a Politico Playbook breakfast event, though he added that he respects the right of states to set their own primary rules.

This assumes a few points that aren’t necessarily in evidence — at least not yet. This push is presumably predicated on the belief that Trump (or other similar outsider/populists) can’t win a general election. Right now that looks like a safe assumption, as there is no data that shows Trump outperforming Mitt Romney in general-election matchups in key states. It’s still early, though, and it’s certainly possible that Trump could beat Hillary Clinton, whose unlikability rivals his own. If Trump wins, doesn’t that moot this point, at least for the party establishment?

Second, Trump’s early wins in primaries didn’t “set the tone of the entire race.” That tone was set much earlier in the primary fight, at least going all the way back to the first debate in August 2015. Observers, analysts, party leadership, and the other candidates simply took far too long in recognizing it. Poll after poll showed Trump dominating a fractured field, pretty much from wire to wire. People assumed it wouldn’t last and that voters weren’t serious about supporting Trump. By the time the primaries started, the only shift in tone that took place was that these people finally took the Trump phenomenon as seriously as the voters.

What about the difference between closed and open primaries/caucuses? It’s true that Ted Cruz did better in closed primaries, but it’s also true that Trump won his share of closed contests, too. Trump won in Florida, Kentucky, Louisiana, Arizona, and romped to huge wins in the five Acela Corridor primary states — all of which held closed primaries. Even where Cruz won closed contests, other factors might explain his success, such as the draw that his ideological conservatism has with Republicans in the West, or his superior retail-politics operation in Iowa. Don’t forget that Cruz’ most spectacular win came in Wisconsin’s open primary — a state where Cruz actually tied Trump among independents.

Conservatives have long pushed for this reform even before the rise of Trump out of frustration with the lack of influence open primaries allows them in nominating a conservative for the ticket. The Trump argument supports their larger argument that the GOP should be the Conservative Party and should exclude others from influencing the nomination. However, this probably wouldn’t have prevented Trump from dominating the 2016 primary, and its overall impact will be to make conservatism and the GOP more insular and marginalized. That might make for a happier nomination result than this year’s, but it will leave lots of persuadable voters unengaged and uninvested in the success of the nominee in the general election.

Conservatism will only succeed by ending its insularity and making itself relevant. That won’t happen by only talking amongst ourselves, nor will it help win elections to spend months only reaching out to Republicans.

Perhaps a better reform would be to do away with the Byzantine delegate-allocation rules and opt for a simple proportional allocation from each state. That makes contested conventions more likely, especially with a crowded field like this cycle, but it then also allows for the better organized and better engaged to have the edge in floor votes.