It'd have to be even more than that. Democrats win D.C. about 90-10 in presidential elections that are about 50-50 nationwide. Given the 90-10 split, Republicans would need a swing of about 41 points to win D.C. If you assume the same swing nationally, the Republican candidate would need to get about 91% of the vote nationwide for the swing in D.C. to equal a victory.
Obviously such a situation will never occur. Therefore, D.C. will never go Republican.
(This all of course assumes we stay under the current party system.)
Uniform national swing almost certainly breaks down at those levels.
You're certainly right. Just for fun, however : John McCain would actually have needed to get 88.56% nationwide to win DC. Barry Goldwater, the republican who performed the best in DC ever (don't ask me why 
), would still have needed 73.97%. Reagan in 1984 (worst performance ever) would have needed 94.6%.
How exactly are you coming up with those numbers Tony?
District of Columbia:
1. Barack H. Obama (Democratic-Illinois) 2008 92.46% Popular Vote
2. John Kerry (Democratic-Massachusetts) 2004 89.18% Popular Vote
3. Lyndon Johnson (Democratic-Texas) 1964 85.5% Popular Vote
4. Walter Mondale (Democratic-Minnesota) 1984 85.38% Popular Vote
5. William J. Clinton (Democratic-Arkansas) 1996 85.19% Popular Vote
6. Albert Gore, Jr. (Democratic-Tennessee) 2000 85.16% Popular Vote
7. William J. Clinton (Democratic-Arkansas) 1992 84.64% Popular Vote
8. Michael Dukakis (Democratic-Massachusetts) 1988 82.65% Popular Vote
9. Hubert H. Humphrey (Democratic-Minnesota) 1968 81.82% Popular Vote
10. James Carter (Democratic-Georgia) 1976 81.63% Popular Vote
11. George McGovern (Democratic-South Dakota) 1972 78.1% Popular Vote
12. James Carter (Democratic-Georgia) 1980 74.89% Popular Vote
Cos yeah, I'm pretty sure Reagan did better in 1984 than McCain did in 2008.
And while Goldwater's numbers were quite impressive for a conservative Republican, Tricky Dick seems to have the best numbers with 21% in 1972.
