So, how can Ronald Reagan lose the 1984 elections? This is going to be difficult, since it was an absolute landslide victory for Reagan. First, the Democrats must run someone who is a little more tempting. Let's say Gary Hart wins the nomination and takes Bill Richardson as a Running Mate (suggestions for anyone else, John Glenn maybe?). Second, Reagan was not exactly popular in 1982/1983 because of the economy. Let's say the economy stays crappy because something (suggestions?).
Let's just assume that Hart/Richardson narrowly manage to beat Reagan, how would a Hart Administration envelop? Hart was anti-nuke so I could see full nuclear disarmement in the late 1980s. It almost happened in OTL, but Reagan backed down.