1. If you repeat a claim about a candidate's character enough times, a non-trivial number of the electorate will believe it, irrespective of the truth of that claim.
2. Fundamentals will often favor the Democrat, but the Dem will somehow run a feckless campaign that squanders this advantage.
3. Running a campaign in a way that appeals to editorial page writers and high-minded pundits = surefire loss. (Related to No. 2 & 4.)
4. Focus groups and issue polling are imperfect ways of predicting voting behavior, as has been proven over and over, yet the Democrats continue to take these results as gospel. Focus groups and poll respondents are forced to make conscious evaluations of ads/issues/candidates and will often tell the interviewer what they are supposed to say, leading to results like respondents claiming to despise negative ads. In reality, a large number of persuadable voters based their voting on less conscious and rational factors, which is heavily influenced by negative messaging. (O Team: please read Drew Westen.)
5. Obama is far savvier in many ways than previous Democratic candidates, yet I'm still feeling deja vu all over again.