On Wednesday, Sanders doubled down on his remarks made at a CNN town hall earlier in the week.
"That is a right we must protect because we know the history of this country. We know that women didn't have the right to vote. We know that African-Americans didn't have the right to vote," Sanders said at a rally in Houston.
Co-host Juan Williams gave credit to Sanders for casting light on the issue.
"Bernie Sanders is moving this conversation incrementally. You don't want to hear it," Williams said.
Co-host Dana Perino argued that Sanders was shifting the conversation to restoring felons' rights after prison because he was scrutinized for saying felons behind bars should be permitted to vote.
"That's not true. I'm not going to take a backseat on felon voting rights," Perino said, saying the topics were separate.
"But, that's not what Bernie Sanders is talking about. That wasn't the initial thing the other day, and him moving the conversation incrementally is to try to save face," Perino argued.
"Let's give Bernie a round of applause. Let the Boston bomber vote. Good job, Bernie," co-host Jesse Watters interjected sarcastically.
Williams defended his point, saying, "You act as if America isn't having this conversation."
"America isn't!" co-host Greg Gutfeld exclaimed.
Gutfeld then jokingly argued that prisoners should be given guns while locked up.
"I should be able to have my gun too, right. If I want my voting rights, I should have my gun rights," Gutfeld said, laughing.