A year ago, when seeking the Republican party endorsement, Fletcher was a party line Republican. When it became apparent that Fletcher wasn't going to win enough Republican votes to finish top two and advance to the general election, he jumped ship from the Republican party and became an independent, saying he no longer fit in with either party. While this was clearly an opportunistic decision, he could make the credible argument that he hadn't changed. The parties were the problem. It was a move that didn't work in 2012, but could've set him up for the future, especially if he was going to seek a non-partisan office again.
And then Fletcher did something which, in hindsight, may appear monumentally stupid. He switched to the Democratic party, a party he criticized as a Republican and as an independent. He completely changed his positions on almost everything. This would've been a canny move if Fletcher was going to try to run for partisan office like the state senate or congress. It's difficult to win such an office without party help.
But mayor is non-partisan and independents are well liked, especially when they criticize both parties. Fletcher, of course, couldn't foresee the mayor resigning and the strong poll indicating he might win.
Of course that's before a campaign, the first shot of which has been taken by the UT San Diego editorial board. They clearly lay out the lines of attack that Fletcher will face in ads, at debates, and, pretty much, at every public event. Almost every position he'll take will completely contradict the positions he took less than two years ago.
He also probably didn't count on a San Diego progressive like councilman David Alvarez getting in the race and drawing support from Democrats. Even people he is counting on are wavering.
Fletcher may start out strong but he's in trouble and it's not hard to see the bottom falling out for him.