There's a reasonably high floor here it seems you can't realistically do anything to drop below. Check https://en.wikipedia.org/wiki/United_States_presidential_app...

Nixon was 24% when he resigned, which is amusingly not actually the lowest, as Truman seems to have twice achieved a spot rating of 22, though Nixon remains the lowest rating for a full year. I wonder what Truman did to be less liked than Nixon. Those were both well after dropping bombs on Japan and before the first H-bomb test.