On Thursday, Sanders posted a video of former President Franklin D. Roosevelt appearing to attack politicians who acted as though they could implement his "New Deal" programs better and without the large price tag.
"Let me warn the nation against the smooth evasion that says 'Of course we believe these things. We believe in Social Security, we believe in work for the unemployed, we believe in saving homes, cross our hearts and hope to die -- we believe in all these things but we don't like the way the present administration is doing them,'" Roosevelt said, apparently mocking his critics.
"'Just turn them over to us. We will do all of them. We will do more of them, we ill do them better, and most important of all, the doing of them will not cost anybody anything.'"
The video seemed to imply that candidates like Hickenlooper falsely claimed they could achieve similar results through policies much different than Sanders'.
Hickenlooper, during a speech in Washington, D.C., on Thursday, directly called out Sanders' brand of Democratic socialism.
“Democrats must say loudly and clearly that we are not socialists. If we do not, we will end up helping to reelect the worst president in the country’s history,” Hickenlooper said, predicting that socialism merely helped President Trump attack Democrats.
“Socialism is the most efficient attack line Republicans can use against Democrats as long as Trump is at the top of the ticket," he said.
His remarks followed Sanders’ impassioned defense of his philosophy Wednesday, when he called on progressives to ignore “massive attacks from those who attempt to use the word ‘socialism’ as a slur.”
Hickenlooper also advocated domestic policies that would avoid the large costs associated with some of the ideas Sanders supported, including the Green New Deal and free college.
“Each candidate, I think, has a responsibility -- however, they want to do it -- to draw that line and say, ‘Hey, I’m not a socialist,’” Hickenlooper said. “Not all the candidates like it when I say that.”
Sanders' response seemed to signify growing tension between centrists and the more progressive wing of the party -- something that popped up in criticisms of 2020 frontrunner and former Vice President Joe Biden.
Delaney, in June, warned of what he called the Democratic Party's growing "intolerance" towards centrist views. That came after progressive icon Rep. Alexandria Ocasio-Cortez, D-N.Y., -- whose endorsement Sanders and Sen. Elizabeth Warren, D-Mass., reportedly sought -- told him to "sashay away" from the race over his opposition to "Medicare for all." That position also provoked boo's when he spoke at the California Democratic Convention.
“Intolerance to different ideas is part of the problem. And that is something I think that is getting very dangerous and concerning in the Democratic Party right now," he said.
Ocasio-Cortez's "Green New Deal," which plays off of Roosevelt's sweeping economic reforms, found support among Biden and Warren, who both referenced the effort in the environmental plans they said they would push as president.
The Associated Press and Paul Steinhauser contributed to this report.