Biden wins.
A July 1988 Gallup poll showed Dukakis leading Bush by 17 points (55-38%). It's virtually impossible for any campaign, no matter how incompetent, to blow a 17-point lead in a month, except of course, for one managed by incompetent political neophyte Susan Estrich. And all of that was
before the infamous tank ride, before airing incomprehensible TV ads, before deciding not to answer misleading charges about his prison furlough program (for the entirety of the election), & so on & so forth.
Or, consider this: Dukakis made more campaign stops in SC (worth 8 EV, where he never had a prayer of winning) than in NJ (worth 16 EV, where he had led until August of 1988). Did Dukakis really think that he was gonna play better in the Deep South than in NJ??
The electoral map
strongly favored the Democratic challenger in 1988; you start off with the 112 electoral votes that Dukakis won (obviously the bare minimum for anyone with a "(D)" after their name) and add to it the electoral votes from CA (47), IL (24), PA (23), NJ (16), MD (10), CT (
, VT (3), & DE (3), & you get a
baseline of 246 EVs for any remotely competent Democrat (e.g., Biden). That leaves you with the following battleground states: OH (23 EV), MI (20), MO (11), CO (
, NM (5), NV (4), & ME (4), which gives Biden a lot more potentially-winnable combinations than Bush. That's a pretty similar position to the one that Obama was in going into 2012, & he was an early 2:1 or 3:1 favorite, so I'd say that's where Biden would be in '88.