Hubert Humphrey and Herbert Lehman supported putting Communists in concentration/detention camps. Granted, they're no McCarthy, but it's rare that we come across politicians as pathologically reckless as Joe McCarthy.
The thing is, the Dems are never going to be the post-War anti-Red Party because New Deal programs, the post-Depression Federal Government, and membership of the Democratic Party from picket lines to the White House are fraught with fellow-travelers. Democrats always noted the community-building potential of far-Leftists, so they incorporated them into the party.
Since the Republicans have spent the last 20 years soaking up every anti-Federal, anti-internationalist, anti-Left john that wasn't already a Dixiecrat, the Red Hordes of FDR's bosom buddy Joe Stalin "infesting" the nation needed to be hounded out. The only counter to this is the rather hollow ring of "fascist" that Leftists throw back, rejecting the more accurate--if less romantic and visceral--epithet of "corporatist."
The Dems cannot go after Reds to the level that Republicans can because they fundamentally cannot afford to without alienating both their principles and a big chunk of their base.