What would it take for Washington DC to vote Republican?

[FerrisBueller86]

Washington DC is so heavily Democratic that no Democratic nominee has ever received less than 74% of the vote.  Marion Barry was elected mayor even after serving time in prison for the infamous cocaine conviction.  Some of you have suggested that DC is so partisan that it would vote for Zell Miller over Lincoln Chaffee.

Because DC has had electoral votes only since 1964, it lacks a voting record under the earlier political alignment.

So what keeps DC so heavily Democratic?  Short of a presidential election taking place when a Republican president has a 90%+ approval rating (like Bush Sr. right after Gulf War I or George W. Bush right after Sept. 11th), what would it take for the Republican nominee to win the 3 electoral votes of Washington DC?

[FerrisBueller86]

The Democrats will never lose DC. Even if there is another realignment, it will stay with the Democrats, just like Kansas and Nebraska have always stayed with the GOP.

So why do these areas keep sticking with the same party?  Many constituencies have changed as the parties have changed.  For example, African Americans were heavily Republican until the FDR administration and then became heavily Democratic as a result of the New Deal.  The reactionaries of the South used to be heavily Democratic and then turned heavily Republican.