FOR THE SECOND TIME in three months, the Obama administration has blocked a state law pushed by Republicans that, using the pretext of a nearly nonexistent problem of voting fraud, discriminates against minority voters by establishing more stringent voter ID rules.

Memo to Virginia Gov. Robert F. McDonnell: You might be next.

In December, the Justice Department moved against South Carolina, saying its new law would suppress turnout among African American voters, who are more likely than other voters to lack identification. On Monday, the department blocked Texas from enforcing a similar measure requiring voters to show photo IDs at the polls, which federal officials said would disproportionately affect Hispanic voters.

Now Mr. McDonnell, his reputation for sensible governance already tarnished by the recent debate over pre-abortion ultrasounds, has a decision to make. Along purely partisan lines, his fellow Virginia Republicans have rammed through a voter ID law only slightly less obnoxious than the ones embraced by Texas and South Carolina. Mr. McDonnell, who has so far remained noncommittal on the measure, should veto it.

The Virginia legislation — a solution in search of a problem — is purely political, designed to give Republicans an edge in a swing state ahead of the fall elections by making voting more difficult for minorities, the elderly and youths — groups that tend disproportionately to lack IDs and to vote for Democrats. And Virginia Republicans barely pretend otherwise.

In a conversation with senior Virginia GOP lawmakers recently, we asked if there was any evidence of a pattern of voting fraud in state elections that would justify more stringent voter ID rules. One state senator said he had “heard” of instances of fraud. We asked our question again: Was there a pattern of fraud that would raise systemic doubts about the integrity of Virginia elections? The senator said no. None of his fellow Republicans contradicted him.

The legislation would reverse a decades-old practice in Virginia that allows voters without identification to cast ballots if they sign a sworn statement attesting to their identity, providing their name appears on the registration rolls. Under the new legislation, those voters could cast only a provisional ballot, which would not be counted unless the voter furnished identification within six days.

Like South Carolina and Texas, Virginia is covered by the Voting Rights Act, which requires the state to prove that any rewrite of voting laws would not adversely affect minorities. True, the Virginia measure allows more leeway than the Texas law, which was the most restrictive in the nation. Virginia’s bill would expand permissible forms of identification to include government checks, utility bills and college IDs, among other documents. But can the state show the legislation has no discriminatory effect?

Even if Republican lawmakers aren’t personally acquainted with people who don’t carry ID, they exist. And provided they are legally registered to vote, they should be allowed to cast their ballots — without encumbrances manufactured by the state.