Some of the L-A-N-G-U-A-G-E poets are good lefties. Ron Silliman edited Socialist Review for a few years. Charles Bernstein's essays from North Point (I think) are a good read. Those two co-wrote a nice travelogue of a trip to Russia sometime in the early 90's. Not having been a lit major would one consider earlier leftish poets like Zukofsky or Olson precursors?
On early 20 C. left poets, btw, see, "Repression and Recovery, " by Cary Nelson. Met him once at a VALB event. Looked like William Everson.