ONE OF the ugliest stains on democracy in this country is the fact that an estimated 2.6 million Americans who have committed a felony are not allowed to vote — even after they have served their sentence. This mass disenfranchisement disproportionately afflicts minority, especially black, communities.

Until recently, almost no prominent Republicans cared to address the problem, seeing little political advantage in registering former inmates — especially minorities — whom they regarded as a largely Democratic electorate. In a dozen mostly GOP-tilting states, some or all felons remain barred from voting even after finishing with parole and probation.

Now some cracks are appearing in that wall to re-enfranchisement. In Virginia, former governor Robert F. McDonnell (R) took a step in the right direction by restoring voting rights for some nonviolent criminals, more or less automatically, once their sentences were served. The state has still not figured out how to spread the word to tens of thousands of former prisoners, but the policy is an act of justice for thousands of convicts from now on.

In another promising sign, Sen. Rand Paul of Kentucky, a Republican weighing a presidential bid, plans to introduce a bill that would restore voting rights in federal elections to nonviolent felons. Mr. Paul acknowledges that he and other Republicans may stand to gain by such legislation, which might soften their image among hostile minority voters. But he also grasps the glaring racial injustice of the status quo.

“There’s a racial outcome to the war on drugs,” he told Politico. “Three out of four people in prison for nonviolent drug offenses are black and brown. White kids are using drugs at the same rate black kids are” but are incarcerated for it far less frequently.

Sen. Rand Paul, R-Ky. speaks at Faith and Freedom Coalition's Road to Majority event in Washington, Friday, June 20, 2014. (Molly Riley/AP)

Mr. Paul’s legislation could plant the seeds of compromise in Congress. A Democrat, Sen. Benjamin L. Cardin of Maryland, has offered legislation that would extend voting rights to all former inmates without regard to the offenses for which they were convicted.

Any federal legislation to re-enfranchise felons would trigger a messy bureaucratic effort in the dozen states that still disenfranchise many or most former prisoners. They would have to create dual voting rolls for federal elections, on the one hand, and state and local elections, on the other. The status quo, which cedes disenfranchisement standards to the states alone, would no longer apply. Nor do all states agree on how to distinguish between violent and nonviolent crimes.

The clear benefit of restoring voting rights and broadening American democracy outweighs the administrative burden. The status quo, under which voting rights are denied to 7.7 percent of black adults and just 1.8 percent of non-black adults, is unacceptable. Mr. Paul’s bill would begin to change that — if other Republicans are willing to follow.