There is no comparison to McGovern. 0bama is closer to socialist/communist leaders from other Nations than any American President/leader. Except maybe Wilson and LBJ and a cheap knock off version of FDR. Oh and Carter. And the currupt influences of a JFK.
But he was a supporter of Henry Wallace in 1948 and was pretty far to the left for his time.
Some political leaders have been pretty soft on Communism -- Wallace, McGovern, Ted Kennedy, etc. -- and some have been pretty close to European socialists -- Obama, Ted Kennedy -- but none of them were actual Leninists or Stalinists so far as I know.