Let the conspiracy theories fly fast and wide on this one. Wellstone was one of the few good guys left in the Senate who supported organized labor, living wages, affordable housing, human rights, and wasand (to the extent that a major party politician can be) a friend to hippies and intellectuals in general. More importantly, he was one of the few congressman to vote against the use of force in Iraq.
Patrick Leahy is basically the only guy left.