What you don't realize is that the Democrats tried their standard tactic in the last election: appeal to enough small segments of the population so as to amass 50% + 1 votes, and take power. They picked Kerry because even though they're not serious about national defense, they needed to convince just enough people to get the 50% + 1 votes. Kery gave them a (questionably) decorated veteran, something they weren't going to get with any of the other candidates.
Unfortunately for them, Kerry simply couldn't overcome questions about his seriousness. Bush, on the other hand, was able to convince a majority that he was serious about defending the borders and bringing the fight to the enemy. And so he won.
Bush's alcoholism, and discredited reports about his Texas Air National Guard service meant nothing by comparison with his willingness to topple regimes that sponsor terrorism. All Kerry had, by comparison, were three Purple Hearts he got for wounds that required band-aids, and which he did/did not throw away, and some questionable stories he could not prove.