He was prime minister from 1997 to 2002 (after Chirac's ill-fated dissolution) so his policies will be the same as in OTL. Now for him to win you need a real change in French politics. Chirac was dominiant during most of the campain and everyon aggres that Jospin did as well as he could considering the circumstances.
Now against Balladur he could have won.
Curiously that might have given him a fighting chance in 2002, as logically the left would have lost the 2000 election which would have make him both the incumbent president and the leader of he opposition to a likely prime minister Chirac (chirac won't do the same mistake twice)