Obama is the first president to visit a federal prison. Here’s why.

On Thursday, President Barack Obama became the first sitting president to visit a federal prison. While that may seem surprising, there’s actually a really simple, if cynical, explanation: Not only are prisoners generally reviled by society, but a great majority of them can’t vote, reducing the incentive for a politician to care about them.

Only two states — Maine and Vermont — allow everyone to vote regardless of criminal record. Most states don’t let people in prison, on parole, or on probation vote, and 10 limit at least some felons from voting after they’ve completed their sentences, according to the American Civil Liberties Union:

So it’s not in politicians’ self-interest to care about what prisoners think — unless the general public cares, which now appears to be the case as advocacy groups push for big cuts in the incarceration rate. In fact, Obama is visiting El Reno, the federal medium-security prison near Oklahoma City, to push for criminal justice reforms that would decrease incarceration, according to the Washington Post’s Juliet Eilperin and Sari Horwitz.

But the disenfranchisement of prisoners and many with a criminal record also has a more sinister effect: It tends to hit black Americans harder, since they’re incarcerated at disproportionate rates. As a result, more than one-fifth of the black electorate has been blocked from voting in some states.

In 2012, more than 5.8 million Americans weren’t legally allowed to vote due to prisoner and felony disenfranchisement, according to data analyzed by the advocacy group Sentencing Project. Several states prohibited 6 to 11 percent of their electorate from voting. And since black Americans are likelier to go to prison, this had a disproportionate impact on the African-American electorate: While the overall disenfranchisement rate didn’t break 11 percent for any state, the black disenfranchisement rate topped 20 percent in Florida, Kentucky, and Virginia.

This is only one of the various collateral effects of prison. Other examples include restrictions on employment and bans on receiving welfare benefits, accessing public housing, or qualifying for student loans for higher education.

So not only does prison deprive people of their freedoms while they’re incarcerated, but the punishment can follow people after they’re out. This extended punishment can sometimes make it much more difficult for ex-inmates to get benefits that would allow them to get a job or education, which might leave them with few options but crime to make ends meet. And since black people are more likely to be affected, these collateral effects can help perpetuate crime in African-American communities.

But there hasn’t been much incentive for politicians to care about these struggles — because, in many cases, the former and current inmates just couldn’t vote.