I voted for Jesse in those '84 and '88 primaries during my days as a Dem mole. If nothing else, Crazy Al may keep the Dems in the left lane, disillusion some black voters (if Al is shunned), and bring out the Republican vote.
At the very least (as others have observed), he wants to take over the Chicago extortion racket from Jesse. (Big Al plays Al Capone and Jesse is Bugs Moran.)