Now the spotlight swings to John McCain, who emerged from Super Tuesday with a commanding lead for the Republican nomination. Even though Democrats will enter the fall campaign as heavy favorites, McCain is fully capable of mounting a serious challenge. But to do so, he has to answer two large questions.

The first is political. Can he appease his conservative critics while continuing his appeal to moderates and independents? Can he run on promises of bipartisan cooperation without alienating ideologues that view such talk as heresy?

The second is personal. Can he satisfy voters that his age, health and temper do not disqualify him from the Oval Office? Can a 70-something cancer survivor, with a long history of flaying his rivals with bitter invective, survive the intense media scrutiny he is about to endure?

All the excitement and energy this year is on the Democratic side. Before the California primary, 150,000 voters registered as Democrats and only 40,000 joined the Republicans. Without campaigning in a meaningless Florida primary, Hillary Clinton drew 160,000 more votes than McCain.

History, however, waves a caution flag. The only successful Democrats since 1968, Jimmy Carter and Bill Clinton, were moderate Southern governors. This year the party will nominate a liberal senator from either New York or Illinois. Before then, Clinton and Barack Obama face weeks, even months, of debilitating civil (or uncivil) warfare. McCain can start healing wounds while his rivals are still picking scabs.