When Mel Martinez reached Jeb Bush last week to tell him that Martinez would shortly announce his decision not to run for reelection to the Senate, Bush expressed no particular interest in succeeding him in Washington. It was early in the morning, and Bush was working out on an exercise machine. Since Martinez's term won't be over until 2010, Bush had plenty of time--months, not weeks--before he'd have to worry about a campaign. But a day later, he told reporters he's considering running.

Bush was wise to disclose his interest. The quick announcement means that no other Republican can gain support for a 2010 Senate race in Florida. Everyone will be waiting for Bush's decision, and the assumption is he's far more likely than not to run. If he does, he will be a strong favorite to win the seat.

Bush's sudden emergence, after two years out of politics, has national significance beyond the possibility he might run for president some day. Republicans, divided and depressed after crushing election losses in 2006 and this year, need unifying leaders with broad appeal. Bush, in his eight years as Florida governor, was popular with all branches of the party. Merely as a candidate, he'd be a focus of Republican attention.

Of course, that's partly because of the question that never goes away: Will Jeb run for president some day? When I interviewed him two years ago in his waning days as Florida governor, I got the impression he wouldn't. "I'm not a big Washington guy,"

But a Senate bid would signal he at least wants to keep the presidential option open. Bush can't afford to stay on the sidelines if he has any hope of being president. That's why a Senate race makes sense. As a senator, assuming he's elected, he would be a national figure. He would also have a few years to fill the one gap in his political experience: foreign policy.

It's true that Ronald Reagan hadn't held elective office for six years when he won the Republican presidential nomination in 1980. But he was the leader of a movement. Bush doesn't have that status, though he is far closer to Reagan ideologically than almost any prominent Republican today and certainly more Reagan-like than his brother or father.

For the moment, Bush's last name may be a hindrance, but that problem should begin to fade after President George W. Bush, his brother, leaves office next month. And it may evaporate altogether as the differences between Jeb and George become clear.

Bush is a small government conservative who often talks about having a "libertarian gene." Neither his brother nor his father, the elder President George H.W. Bush, has anything of the kind. "There should not be such a thing as a big government Republican," Jeb Bush told Politico after the November election, differentiating himself from his brother in a none-too-subtle way.