Other Democrats, including Gov. Jack Markell of Delaware, told the New York Times that that Sanders could endanger Democrats running in more purple states, like Pennsylvania and Wisconsin, where Democrats are hanging their aspirations to take back the Senate in 2016.
Recent polls have shown Sanders gaining momentum in early states. A CNN poll Tuesday showed him leading Clinton by 27 points in New Hampshire and Des Moines Register poll found him closing the gap in Iowa.
Wednesday, the criticism continued as McCaskill stood by her concerns about Sanders. In an interview with NBC, McCaskill said it was "absolutely impossible" for him to win in her home state of Missouri. She also warned that Sanders was untested. While Republicans have targeted Hillary Clinton in attacks since they hit the campaign trail, Sanders has so far been left unscathed.
"Bernie has not felt those chainsaws and they would come out like a vengeance if he were our nominee," McCaskill told MSNBC Wednesday. "It is very hard for most Americans to see how socialism would cure the problems that we are facing right now."