VIRGINIA REPUBLICANS, more hostile than ever to moderates in their ranks, have become an increasingly exclusive club.

Their preferred means of enforcing that exclusivity and banishing centrist candidates are scantily attended party conventions, which they like to call mass meetings. Unlike primary elections, these attract a self-selecting group of the most conservative, ideologically committed voters.

This has not been a winning strategy. In 2008, the Virginia GOP’s decision to hold a convention, rather than a primary, to choose its nominee for the U.S. Senate forced a moderate, then-Rep. Thomas M. Davis III, to withdraw. The convention nominated a conservative, James S. Gilmore III, who lost in a landslide to Mark R. Warner.

The party’s hard-liners ran the same play last year in the runup to statewide elections, opting for a convention that prompted the leading moderate gubernatorial hopeful, Lt. Gov. Bill Bolling, to bow out. The Republican convention nominated the most conservative statewide slate in recent history — which, barring a reversal in the race for attorney general, was swept in last month’s general election.

Perhaps hoping the third time’s the charm, the GOP is at it again — this time to block a moderate Republican from running in a special election. The hard-liners’ target this time is Del. Joe T. May, a businessman who has served in the House of Delegates for 20 years but was defeated in a Republican primary last summer.

Mr. May’s sins were to vote for some restrictions on gun use (though he is generally pro-Second Amendment) and a transportation funding bill — signed by a Republican governor — that will raise taxes.

Undaunted, he announced last week that he would seek the party’s nomination in the special election to replace Sen. Mark Herring (D) of Loudoun County, assuming Mr. Herring survives a recount and becomes attorney general. In response, local GOP honchos immediately decreed that the nominee would be picked at a mass meeting, not a primary — a tactic that dooms Mr. May’s chances.

In fact, there is nothing “mass” about the mass meeting they have in mind. By holding the meeting at one high school on one weekday evening, they would ensure that turnout is limited to a few hundred party activists. (By contrast, when Democrats held their special election last month, with polls open all day at three venues, more than 1,100 voters cast ballots, selecting Jennifer Wexton as the nominee.)

In the bargain, Republican insiders arranged for the meeting to take place far from Mr. May’s electoral stronghold, in a place advantageous to a conservative rival, a party official named John Whitbeck. (Mr. Whitbeck is mainly known beyond his neighborhood for telling an anti-Semitic joke at a tea party rally, then dragging his feet before apologizing for what he called “a lighthearted attempt at humor.”)

It’s anyone’s guess whether Mr. Whitbeck will be more successful than the other hard-liners chosen in exclusive Republican conventions. What’s clear is that the party’s tent has shrunk, and continues to shrink, thanks to such escapades. Meanwhile, Mr. May has severed his ties to the party and announced he will run in the special election as an independent.