Charlie Crist's last-minute invitation to speak at the Democratic convention will serve Barack Obama's purposes well. Crist, a former Republican governor of Florida and an Independent candidate for Senate in 2010, provides a nice foil to the party-switchers of whom Republicans are so proud -- most notably former Rep. Artur Davis, D-Ala.

Party-switchers have given Republicans a PR boost. They even helped the GOP take solid control of state legislatures in both Louisiana and Alabama in the last cycle. But Crist is also a bit of an own-goal. He is a damaged figure, who would have been happy to go on a Republican forever, had it served his career.

Crist's 2010 Senate campaign was an exercise in political malpractice. A sitting governor, he began as the prohibitive favorite for the Republican Senate nomination. In mid-2009, when I first met Marco Rubio, I believed it wishful thinking to take him seriously. I began our interview by asking whether he wasn't just running to raise his profile for some future race -- maybe for a South Florida House seat.

How wrong I was. Less than a year later, Crist was a thoroughly desperate man. Slipping in the GOP primary polls, his campaign became so negative that he often served as his own mudslinging messenger. His low-point probably came in a March 2010 interview with Greta Van Susteren, in which the perpetually well-tanned Crist accused Rubio of getting his back waxed.

When he finally bailed out of the GOP to seek an independent bid for Senate, just before the deadline, he was already a political dead man walking -- although it took several months for the conventional wisdom to grasp this fact. He knew he could not beat Rubio in the primary, so this was his best chance of survival.

But then the squeeze began coming from all directions. In June, Crist's handpicked Republican Party chairman -- whom the state's conservatives despised -- was arrested for self-dealing with party money. In late September, the state Democratic Party began running a blistering ad that contained no commentary at all. None was needed -- all they had to do was quote from all the conservative posturing Crist had done before his decision to defect: "I'm about as conservative as you can get ... I'm a Jeb Bush Republican ... President Bush is a leader of courage and conviction ... I was impressed at Gov. Palin being picked. I watched her speech today, I was very impressed ... I'm a pro-life, pro-gun, anti-tax Republican ... I think it's important for people to understand who the true conservative is in this race, and it's Charlie Crist."

All of these quotations now make Crist look silly. So do the tweets he sent out, trashing Obama and Obamacare: "Pres. Obama and Dems ignored the will of the ppl and passed a partisan-gov't run HC bill." "Pres. Obama needs to support NASA with more than just a photo op."

Crist's September 2009 comparison of Obama to Carter will also live on: "They wanted a change back in 1976. You remember? Richard Nixon had been president. That ended. Gerald Ford took over. The people decided they wanted a change. They got one -- Jimmy Carter. Four years later, they took care of business -- Ronald Reagan. It may happen again."

Crist was crushed in 2010. Some polls show a shallow willingness among Floridians to resurrect his political career -- in May, a Florida Opinion Research poll showed him beating Republican Gov. Rick Scott by double digits. But what happens when his rivals in a Democratic primary run the tape of him trashing Obama?

There is a lesson here for political opportunists. Party switches made sense for the conservative Democrats who went to the GOP in the 1990s. They probably made sense for Northeastern Republicans with liberal principles, like Jim Jeffords and Lincoln Chafee, who both left the GOP last decade.

But for Crist, it's different. He doesn't have any principles. He may have gotten the Democratic convention speaking slot he wanted, but he will probably never win the Democrats' love. As hard as it is to stand on principle, it's a much harder political world for someone who doesn't believe in anything.

David Freddoso ( is the editorial page editor for The Washington Examiner. Follow him on Twitter at @freddoso.