Sen. Bernie Sanders on Tuesday unequivocally doubled down on his position that prisoners should have the right to vote—as dozens of civil rights groups urged every other 2020 Democratic presidential candidate to adopt the same stance.

"At a time when voting suppression is taking place all across the country, we must make it clear that casting a ballot for American citizens is not a privilege. It is a right."

—Sen. Bernie Sanders In an op-ed for USA Today, the Vermont senator noted that prisoner disenfranchisement disproportionately harms poor people of color and is rooted in the "legacy of slavery and continuing racist attitudes post-Jim Crow."

"Indeed, our present-day crisis of mass incarceration has become a tool of voter suppression," Sanders wrote. "Today, over 4.5 million Americans... have lost their right to vote because they have served time in jail or prison for a felony conviction."

Sanders has faced continued backlash from right-wing media outlets, Republican lawmakers, and fellow Democratic presidential candidates since he expressed support for allowing prisoners to vote in a CNN town hall earlier this month.

But in his op-ed Tuesday, the senator from Vermont—a state that allows inmates to vote from prison—said he makes "no apologies for that position" because "voting rights for all citizens is a basic principle of democracy."

"The point here is simple," wrote Sanders. "At a time when voting suppression is taking place all across the country, we must make it clear that casting a ballot for American citizens is not a privilege. It is a right. If you're an American citizen who is 18 years or older you must be able to vote, whether you're in jail or not."

If we are serious about calling ourselves a democracy, we must firmly establish that the right to vote is an inalienable and universal principle that applies to all American citizens 18 years and older. Period. 1/ https://t.co/d8H6Cntn3Q — Bernie Sanders (@BernieSanders) April 30, 2019 When we look at the history of why our country has banned incarcerated people from voting, we must understand that the efforts to rob citizens of their voting rights was a legacy of slavery and continuing racist attitudes post-Jim Crow. 2/ — Bernie Sanders (@BernieSanders) April 30, 2019

Every 2020 presidential candidate should join Sanders in taking a stand for the right of prisoners and felons to vote, a coalition of more than 70 rights groups including the ACLU, the Drug Policy Alliance, and Color of Change said in an open letter on Tuesday.

Sanders is the only 2020 contender who has expressed support for allowing prisoners to vote.

Highlighting the "growing movement against felony disenfranchisement" nationwide—such as in Florida, where voters last year passed a constitutional amendment to restore the voting rights of 1.4 million people with past felony convictions—the advocacy groups asked: "Why disenfranchise people in prison to begin with? Why not let them continue to vote while they are incarcerated?"

"Ensuring that ​all Americans can vote is not just a vital affirmation of our national character, but an important policy to enhance public safety and reduce recidivism," the groups wrote. "We thus ask each of you to publicly commit to ending felony disenfranchisement and to call for the restoration of voting rights for all citizens, regardless of their criminal history."

Read the full letter: