Armored Diplomacy said:
With a POD no further than 1945, prevent the decline of Detroit.
Would you accept 1944? A quite small change in the G.I. Bill of Rights, to discourage only buying new houses (in new 'burbs

), or also encouraging renovation with the same lo-interest loans, would be a big help.
Lobbying to eliminate the mortgage interest deduction would be good, too.
(Yes, these affect more than Detroit...but Detroit got bitten by these harder than most cities.)
A ban on insurance company redlining would be good, too. (That's a state issue AIUI.)
Changing the state tax laws to discourage 'burbs subsidized by inner cities, or so farmers don't end up paying insanely high taxes (& selling out to developers), would be a big help, too. (Also a state or local matter.)
Improving the overall build quality of Detroit cars starting in the '50s or '60s would be a big, big help. (There's a reason a Lincoln owner set his on fire

in the '70s, & it's not high gas prices.

)