When libertarian Republicans go on about the “tyranny” of the federal government, as Kentucky Sen. Rand Paul is prone to do, I tune out. But not today. Paul has been talking for a while about how his conception of tyranny extends to long, draconian prison sentences for mostly poor and black offenders. Now he is introducing a bill that would restore voting rights to nonviolent ex-felons in federal elections. This bill is not about to become law any time soon. But give Paul credit for standing on principle even though he and his party would hardly benefit.

If Congress really re-enfranchised ex-cons across the land, it would help Democrats. It would probably be enough to swing a close Senate race in some states—or to push Florida into the D column in a presidential election. In 2010, according to this policy brief by the Sentencing Project, 5.85 million people across the country couldn’t vote because they were either in prison or had a felony record (which in 12 states also disqualifies you at the polls). Consider only people who have completed their sentences, and the number drops to 2.6 million. But the majority are nonviolent (Paul’s limiting factor) and 1.3 million of them live in Florida. The state is 1 of 3 in which more than 1 in 5 black adults are disenfranchised. The other two states on that list are Virginia—another swing state—and Paul’s own Kentucky.

To state the obvious, if these ex-cons voted, they would break for Democrats. “African-American voters are wildly overrepresented in criminal justice populations. African-American voters also historically favor Democratic candidates,” says Christopher Uggen, a sociologist at the University of Minnesota. Uggen and Jeff Manza co-wrote an article for the American Sociological Review in 2002 in which they estimated turnout for disenfranchised ex-cons. Given factors like socioeconomic status—most ex-cons aren’t well off—they figured turnout would be about 35 percent for presidential elections, and 24 percent for the Senate during off-year contests. Plug in those numbers for Florida, and you see the risk here for Republicans. “There’s no question this could affect Florida’s electoral votes,” Marc Mauer, executive director of the Sentencing Project, said when I called him. “Even if only 10 percent of those who were newly eligible actually voted, and that’s very low, their participation could easily affect the outcome of a presidential contest in a state where the vote is close. Or a Senate race.” Mauer is right: 10 percent is very low. Uggen’s numbers show that, and so does the fact that in the most recent presidential election, black turnout was 66 percent.

So why is Paul pushing for a bill that could actively hurt his party? “Even if Republicans don’t get more votes, we feel like we’ve done the right thing,” Paul told Politico. This sounds like Paul’s (qualified) support for immigration reform: He’s behind it even though in the short term, it’s probably a loser for Republicans.

I don’t mean to sound naive here about Paul’s motives. He sometimes cultivates renegade Tea Party independence, and I realize that he is also appealing to swing voters: moderates who like it when conservative politicians sound concerned about poor people and minorities. And maybe that’s good for the image of the Republican party overall: Rand Paul, softening agent. Uggen says he did a poll a few years ago and found resounding majority support for letting ex-felons vote. But how many of those people care enough about the issue to vote for Paul based on it? That number has to be tiny. And while it’s possible to argue that Republicans have to move toward immigration reform for their long-term survival, given the rising Latino population and the shrinking white one, felon disenfranchisement just doesn’t have the same grip.

Uggen has a different theory to explain Paul’s political calculus, or at least his behavior. He starts with the traditional advantage Republicans have on being seen as tough on crime, and then notes that, in the last 15 years, some Republican governors have signed bills re-enfranchising felons. They include George W. Bush, who signed a bill in Texas allowing ex-cons who’d completed their sentences (including probation) in 1997 to vote. “Here’s how I think about this: You need some degree of political cover to get out in front on this issue,” Uggen said. “It helps if no one will question whether you’re tough.” He also points out that Paul has tapped into a real libertarian streak. “When I went on conservative radio for my book, Locked Out, the audience was not unsympathetic to the idea that the government shouldn’t be too quick to take away voting rights,” he said. “And by the way, they shouldn’t take away the guns either. I think that clears some space for people like Paul to act on principle.”

It’s worth pointing out, though, that Paul is the sole sponsor for his bill. In Florida in 2011, Republican Gov. Rick Scott went the other way and tightened voting restrictions on former felons, in spite of criticism about the number of black people he was barring from the polls. Paul has more company from fellow libertarians Ted Cruz and Mike Lee in pushing for sentencing reform. This is the larger fight that felon disenfranchisement is a part of: addressing mass incarceration by lowering or eliminating mandatory minimum sentences, especially for nonviolent drug offenders. “I’m talking about making the criminal justice system fair and giving people a second chance if they served their time,” Paul said in February at a gala for the conservative American Principles Project. Give him, and Cruz and Lee, credit for being part of this push. Sentencing reform has justice on its side and budgetary common sense, too, given the huge sums it takes to keep prisoners locked up for years. Too bad other Republicans won’t support that cause, or go for giving former felons the vote either.