The Socialist Party of America announced in their October 2009 newsletter that 70 Congressional democrats currently belong to their caucus.
This admission was recently posted on Scribd.com:

American Socialist Voter–
Q: How many members of the U.S. Congress are also members of the DSA?
A: Seventy

Q: How many of the DSA members sit on the Judiciary Committee?
A: Eleven: John Conyers [Chairman of the Judiciary Committee], Tammy Baldwin, Jerrold Nadler, Luis Gutierrez,
Melvin Watt, Maxine Waters, Hank Johnson, Steve Cohen, Barbara Lee, Robert Wexler, Linda Sanchez [there are 23 Democrats on the Judiciary Committee of which eleven, almost half, are now members of the DSA].

Q: Who are these members of 111th Congress?
A: See the listing below

Co-Chairs
Hon. Raúl M. Grijalva (AZ-07)
Hon. Lynn Woolsey (CA-06)

Vice Chairs
Hon. Diane Watson (CA-33)
Hon. Sheila Jackson-Lee (TX-18)
Hon. Mazie Hirono (HI-02)
Hon. Dennis Kucinich (OH-10)

Senate Members
Hon. Bernie Sanders (VT)

House Members
Hon. Neil Abercrombie (HI-01)
Hon. Tammy Baldwin (WI-02)
Hon. Xavier Becerra (CA-31)
Hon. Madeleine Bordallo (GU-AL)
Hon. Robert Brady (PA-01)
Hon. Corrine Brown (FL-03)
Hon. Michael Capuano (MA-08)
Hon. André Carson (IN-07)
Hon. Donna Christensen (VI-AL)
Hon. Yvette Clarke (NY-11)
Hon. William “Lacy” Clay (MO-01)
Hon. Emanuel Cleaver (MO-05)
Hon. Steve Cohen (TN-09)
Hon. John Conyers (MI-14)
Hon. Elijah Cummings (MD-07)
Hon. Danny Davis (IL-07)
Hon. Peter DeFazio (OR-04)
Hon. Rosa DeLauro (CT-03)
Rep. Donna F. Edwards (MD-04)
Hon. Keith Ellison (MN-05)
Hon. Sam Farr (CA-17)
Hon. Chaka Fattah (PA-02)
Hon. Bob Filner (CA-51)
Hon. Barney Frank (MA-04)
Hon. Marcia L. Fudge (OH-11)
Hon. Alan Grayson (FL-08)
Hon. Luis Gutierrez (IL-04)
Hon. John Hall (NY-19)
Hon. Phil Hare (IL-17)
Hon. Maurice Hinchey (NY-22)
Hon. Michael Honda (CA-15)
Hon. Jesse Jackson, Jr. (IL-02)
Hon. Eddie Bernice Johnson (TX-30)
Hon. Hank Johnson (GA-04)
Hon. Marcy Kaptur (OH-09)
Hon. Carolyn Kilpatrick (MI-13)
Hon. Barbara Lee (CA-09)
Hon. John Lewis (GA-05)
Hon. David Loebsack (IA-02)
Hon. Ben R. Lujan (NM-3)
Hon. Carolyn Maloney (NY-14)
Hon. Ed Markey (MA-07)
Hon. Jim McDermott (WA-07)
Hon. James McGovern (MA-03)
Hon. George Miller (CA-07)
Hon. Gwen Moore (WI-04)
Hon. Jerrold Nadler (NY-08)
Hon. Eleanor Holmes-Norton (DC-AL)
Hon. John Olver (MA-01)
Hon. Ed Pastor (AZ-04)
Hon. Donald Payne (NJ-10)
Hon. Chellie Pingree (ME-01)
Hon. Charles Rangel (NY-15)
Hon. Laura Richardson (CA-37)
Hon. Lucille Roybal-Allard (CA-34)
Hon. Bobby Rush (IL-01)
Hon. Linda Sánchez (CA-47)
Hon. Jan Schakowsky (IL-09)
Hon. José Serrano (NY-16)
Hon. Louise Slaughter (NY-28)
Hon. Pete Stark (CA-13)
Hon. Bennie Thompson (MS-02)
Hon. John Tierney (MA-06)
Hon. Nydia Velazquez (NY-12)
Hon. Maxine Waters (CA-35)
Hon. Mel Watt (NC-12)
Hon. Henry Waxman (CA-30)
Hon. Peter Welch (VT-AL)
Hon. Robert Wexler (FL-19)