Bernie Sanders accused Republicans of being "political cowards" who want to restrict the right to vote while speaking at a Democratic candidates' forum in South Carolina Friday night.

MSNBC's Rachel Maddow asked Sanders, the Vermont senator and 2016 presidential candidate, about voting rights becoming a "partisan issue." She began to say that Democrats were expanding access to voting while Republicans were restricting it when Sanders cut her off.

Sanders said the GOP was actually violating the constitutional right to vote. "What Republicans are doing is so un-American, it is so outrageous," Sanders bellowed.

Mentioning his lengthy career running for office, Sanders said, "It has never occurred to me to deny someone the right to vote because they won't vote for me." He said Republicans who would pass voter ID laws and other things he claimed would suppress voting by predominantly Democratic groups are "political cowards."

"If they can't face a free election, they should get another job," he added to applause.

The senator suggested he would be open to a constitutional amendment to automatically register Americans to vote on their 18th birthday.

The Democratic forum took place at Winthrop University in Rock Hill, S.C.