These people are members of the Progressive Cacaus. about four years ago the DSA listed them as members, with a link to the Progressive Cacaus membership list. A link to the DSA web site was posted here on Freerepublic, Rush, and many other talk show hosts talked about it. The Socialists started getting confronted by constituents, it didn't take long until any mention of the Progressive Cacaus was removed from the DSA web site. Their canned answer was that they didn't, and never had belonged to any organization with the word Socialist in it's name.
A DSA representative named Llewellyn was interviewed on C-SPAN a few years back and confirmed that only two members of Congress are card carrying members - they are Major Owens (NY) and Danny Davis (IL). He also confirmed that John Sweeney, the AFL-CIO commie rat leader is also a member. The latter fact was also reported in the Washington Times years ago. I have heard a few times that Sweeney is also affiliated with both the French and Italian communist parties but I can't find a hard reference to prove that - wish I could.
That C-SPAN interview was discussed in a few threads back then and you might find it in the FR archives, and someone probably has a tape of it. C-SPAN certainly has it, but it's a few years old and probably would require some work to get it from them if you really wanted it.
Bernie Sanders is no longer the chair of that "progressive caucus", a POS named Dennis Kucinich is. I am particularly PO'ed because thanks to REPUBLICAN redistricting in Ohio which they blew big time I am going to get stuck with this RAT, along with many fine Republican communities who will have absolutely no voice in DC anymore.
While they may not be card carrying members of DSA (at least Owens and Davis are honest enough to admit it) it doesn't take a genius to figure out that the "progressive caucus" is the de facto legislative arm of the DSA. There is all kinds of proposed legislation by these guys that has DSA's fingerprints all over it.