T AMPA — Former Gov. Charlie Crist lobbed a bombshell announcing his support of President Obama just as the Republican National Convention was about to begin this week.

Many Republicans at the convention weren’t surprised by Mr. Crist’s op-ed published in his hometown paper, The Tampa Bay Times. They have viewed Mr. Crist as a turncoat opportunist ever since he and the president hugged during an event to unveil stimulus funding that saved hundreds of thousands of jobs in Florida for police, teachers, firefighters and other public employees at the worst point in the recession.

Gov. Rick Scott told The Herald Editorial Board on Sunday that he was “shocked” his predecessor would come out for the Democratic president just as Floridians were dealing with approaching Tropical Storm Isaac. Such are the political storm winds with Hurricane Charlie.

But Mr. Crist, a lifelong Republican until he turned independent after his loss to Marco Rubio in the U.S. Senate primary two years ago, has never been easily labeled. That, in essence, was the basis for his popularity that crossed party lines until “The Hug,” when Republicans became incensed.

In the 1990s Mr. Crist was a tough law-and-order state senator, pushing for felons to serve 85 percent of their sentences before they could be eligible for parole. Later, as attorney general, he was a consumer advocate, freezing utility rates, and a civil rights populist, dredging up old racially-inspired murder cases to prosecute and supporting laws requiring paper records of electronic ballots when it was found that some votes were undercounted in black precincts.

He burnished his environmentalist credentials by pushing for the costliest land-buying program to save the Everglades — a deal that soured when the economy tanked.

Mr. Crist may have put the Republican Party on the spot with his endorsement of Mr. Obama, but he also put Florida’s Democratic Party on the defensive, as the Democrats rightly criticized the former GOP governor’s relationship with Ponzi schemer Scott Rothstein and former GOP chief Jim Greer, accused of bilking party coffers.

Criticism of Mr. Crist’s political opportunism aside, he raises a crucial issue for Mitt Romney as he tries to show the nation who he is and what his party stands for. As governor of Massachusetts, Mr. Romney had to compromise in a heavily Democratic state. If he is to win this race in a sharply divided nation he must show Americans that he can stick to his principles of “economic freedom” and “individual opportunity” while compromising with shared sacrifice to reduce the national debt, a symbolic clock that the RNC has ticking at its convention hall.

Mr. Crist offered this assessment to Republicans: “Across Florida, in Washington and around the country, I’ve watched the failure of those who favor extreme rhetoric over sensible compromise, and I’ve seen how those who never lose sight of solutions sow the greatest successes. . . . The truth is that the party has failed to demonstrate the kind of leadership or seriousness voters deserve.”

He’s right. In the most recent CNN poll of likely voters surveyed from Aug. 22-26, President Obama holds a narrow lead of 50 percent to 46 percent for Mr. Romney in Florida, with a margin of error of 3 percentage points.

Mr. Crist was on point: Shared sacrifice and shared compromise will raise America up not tear it down in divisive rhetoric.