Last Presidential Election where you would have voted for the other party

[Blair]

For the UK 1983, where without hindsight I would have voted for the SDP. The only situation I could see voting Tory would be a 2nd preference for London Mayor if Labour ran someone awful (although I would have happily voted for Red Ken in 2008/2012)

For the US I'm going to be boring and, like everyone say Eisenhower 1952. Interestingly enough Bobby Kennedy worked for Stevenson's campaign in '56 and still ended up voting for Ike.

Would probably have been a pissed off Kennedy Democrat in 1980 and flirted with voting for Anderson