When the Democrats gather at the Windy City — so named for its political palaver by an erstwhile editor of the Sun — to present their ticket to the nation, they will do so with political fortune gusting in their favor. At least if the pollsters have it right. Vice President Harris has gone from a ragged number two to a frontrunner. Governor Walz, once a coach, no doubt feels he has a lead at the fourth quarter. Yet Democrats have not always prospered at Chicago.