How to win a presedential election if you're a democrat: (Alternate title - The Republican will always win unless...)
1. Be from the South.
Democrats from the South are the only kind of democrats that can win an election. That's because you need those Dixie votes, and Dixie will only vote Dixie. I call your attention to the last two democratic presidents - Carter and Clinton. Southern democrats are raised in a right-wing atmosphere, and they've learned how to talk about democratic platforms to republicans and not offend anybody. Yankee democrats are used to everybody around them being democrats, so they just say whatever want. Yankees might have the edge within the party, but on the national level, a Southerner is your only hope of getting any Southern or battleground state. (Sorry Edwards, but VP just doesn't matter on this call, it's got to be the president)
2. Be Interesting
It doesn't really matter where you're from or what party, if you're boring you'll never succeed in politics. It wins and loses elections - take a look at Gore and Kennedy. Gore may have been from Tennessee, but damn was he dull. And what Kennedy lacked in geographic heritage, he made up for in charisma. (Sorry Kerry, but you remind people of a cross between Herman Munster and Lurch.)
3. Eliminate the Third Party Threat
In this country, half the people are Republican, and half are either democrat or third party. You need the independents, Republicans don't. This nation is naturally more conservative, and the GOP candidate will be elected unless you get the swing vote and battleground states. People who would otherwise vote democrat vote independent just because it's there. Independent candidates steal those votes from the democratic candidate, leaving the door open for the republican to win. Sling mud at the middle, not the right.
4. Be damn good at what you do
Only six democrats were elected to the presidency in the twentieth century (before that the terminology was all switched up): Wilson, Roosevelt, Truman, Kennedy, Carter, Clinton. Johnson doesn't count; he wasn't elected. The last three I've already explained - Southern and/or charming. As for the first three, well, there was no significant third party in their time, plus they had other factors like major wars and depressions and what-not to play off of. If you can find you one of them (not this fake war we're in right now, but a real problem) you might be able to convince some people to vote for you. Otherwise, the Republican always wins by default.