Next month’s elections in Virginia coincide with a singular moment in U.S. history, in which one major party has turned against accepting the results of free and fair elections. That momentous juncture poses a character test for all Republicans, which turns on this question: Will they stand against the assault on democracy’s most basic precept, or will they tolerate it? Glenn Youngkin, the GOP gubernatorial nominee in Virginia, has failed that character test.

A wealthy private equity executive turned political newcomer, Mr. Youngkin has run what amounts in some ways to a conventional Republican campaign, seeking at once to court rural White conservatives and swing-voting suburban moderates. But he also has indulged and encouraged Republicans who have swallowed former president Donald Trump’s lie that last year’s presidential election was stolen and that American elections are not to be trusted.

Few stances could be more subversive to the American experiment or more corrosive to our pluralistic system’s fundamental legitimacy. Few shine so bright a spotlight on a candidate’s courage and commitment to the Constitution, or lack thereof.

It seems likely that Mr. Youngkin knows that U.S. elections, including last year’s presidential contest, have been largely free of any significant fraud or cheating, and that to suggest otherwise is flat-out dishonesty. No elections are immaculate, but there is zero credible evidence that conspiracies and malfeasance in voting have altered the outcomes of high-profile U.S. electoral contests in recent decades.

Nonetheless, for months, as he sought the gubernatorial nomination — and while Mr. Trump promoted those lies and refused to concede the results of the election — Mr. Youngkin refused to acknowledge that President Biden was fairly elected, by a comfortable margin, or that allegations that the 2020 election was stolen were baseless. To the contrary, during those months Mr. Youngkin’s No. 1 policy proposal, and the only one for which he supplied any detail, was to establish a state commission on election integrity, an idea that winked at the prevalent, and baseless, idea among Republicans that elections are fraudulent.

It was only after he secured the nomination that Mr. Youngkin finally said, grudgingly, that Mr. Biden is the legitimate president. Since then, he has rarely submitted to challenging interviews or media appearances, but he did finally acknowledge, under direct questioning, that past Virginia elections have not been marred by fraud — nor did he expect cheating in this one.

Yet both before and after those statements, he undercut them by continuing to flirt with pernicious lies. He dodged a question about whether, had he been in Congress, he would have certified Mr. Biden’s election; then, under pressure, he conceded it had been fair. Unsolicited, he raised questions about whether Virginia’s voting machines can be trusted by insisting that they be audited — which they already are. He attended an “election integrity” rally at Liberty University in Lynchburg, from which journalists were excluded.

When asked by a hopeful GOP voter whether the courts might reverse the 2020 election results, Mr. Youngkin dodged, saying that courts move slowly and “it’s unclear” whether they might reinstall Mr. Trump as president. When another voter asked about fraudulent ballots cast by dead people — another falsehood popular among Republicans — Mr. Youngkin offered sympathy and tacit agreement, urging tighter voting rules and pledging as governor to “make some reforms.”

This is not an everyday campaign dispute. We might disagree with Mr. Youngkin on Medicaid expansion, say — he termed it “sad,” though it extended health insurance to hundreds of thousands of Virginians who lacked it — without arguing that his stance is disqualifying. But at a moment when democracy itself is under assault, Mr. Youngkin chose to dignify a fundamental fiction that is subverting our system, rather than stand up squarely for the truth. In so doing, he proved himself unfit for office.