All of the Democrats running for president favor reforms to expand the right to vote , but the candidates are divided on one emerging question: Should people in prison, even ones convicted of the most heinous crimes, be able to vote?

The issue seemingly came out of nowhere. For months, the debate has centered on whether people should be able to vote once they leave prison. But now, activists are taking it a step further.

Sen. Elizabeth Warren (Mass.) was the first Democratic presidential candidate to go on record, albeit without saying yes or no, when HuffPost asked her about her position on the matter in March.

While theyre incarcerated, I think thats something we can have more conversation about, she said.

Sen. Bernie Sanders (I-Vt.) was the first one to take a stand and endorse voting while incarcerated. The issue came up at a town hall in Muscatine, Iowa, in early April. Sanders appears to be the first candidate seeking the nomination of a major party ever to back the idea that prisoners should be allowed to vote.

The debate drew increased attention after Sanders , Sen. Kamala Harris (Calif.) and South Bend, Indiana, Mayor Pete Buttigieg were asked at CNN town halls this week whether they believed terrorists like the Boston Marathon bomber should be allowed to vote in prison. Harris expressed openness to the idea, while Buttigieg, echoing the position of many other Democrats running, said people should have their voting rights restored once they complete their criminal sentences.

Former Rep. Beto ORourke (Texas) and former Housing and Urban Development Secretary Julin Castro both said earlier this week that they are open to allowing nonviolent offenders to vote. ORourkes current position may reflect the power of raising an issue: A spokesman had previously told HuffPost that ORourke only supported restoring someones voting rights once they were released from prison.