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For most of the nation's history, headliners on the presidential tour performed to the same basic beat, while varying the lyrics. They were all established men, invariably WASPs. Not this time. The diversity of the fields in both parties is nothing short of startling and will test whether Americans are ready to vote for ...

A woman? Hillary Rodham Clinton, with her campaign juggernaut, is by far the most plausible female candidate in American history. An African-American? There have been black candidates before, but none has accumulated as much momentum as Barack Obama. A Hispanic? Bill Richardson, with the thickest résumé in the field, has lagged from the start but could end up on the Democratic vice-presidential short list. A Mormon? Amid doubts within his inner circle about the wisdom of doing so, Mitt Romney tackled the issue of his religion head-on this month. A Baptist preacher? Mike Huckabee's startling rise in recent weeks has obscured the fact that politics is actually his second career, started after two decades spent in the pulpit. A septuagenarian? John McCain, who regularly jokes that he's "older than dirt," would be 72 by inauguration day in 2009, older than any newly elected president before him. A thrice- married Catholic? A candidate's Catholicism hasn't been a major issue since 1960, but Rudy Giuliani's famously messy life could remain a hurdle.

Both parties' fields can be separated into two tiers, the front-running stars -- Who's ahead? Depends on the day -- and strictly backup singers who appear to have virtually no chance to win, regardless of the passion of their supporters.

THE DEMOCRATIC STARS

NEW YORK SEN. HILLARY RODHAM CLINTON

High notes: Disciplined, a genuine policy wonk, her husband. Off key: Seen as cold and calculating, legendarily polarizing. Stage presence: Not a natural politician, has strived to attain warmth.

FORMER NORTH CAROLINA SEN. JOHN EDWARDS

High notes: Fiery populist rhetoric, focusing campaign on the nation's poor. Off key: A thin résumé, spending as much time running for president as serving in the Senate. Stage presence: Alternating between sunny and angry, can leave voters wondering if he's genuine.

ILLINOIS SEN. BARACK OBAMA

High notes: Charismatic with an obviously sharp intellect. Off key: Lack of government experience an obvious target, inability to live up to advance hype. Stage presence: Occasionally mesmerizing, sometimes professorial.


THE REPUBLICAN STARS

Former New York City Mayor Rudy Giuliani

High notes: Became "America's Mayor" in the wake of 9/11, leveraging that into a candidacy almost entirely about terrorism. Off key: Is that enough? Will his checkered background matter? Stage presence: Will New York edginess play in the heartland?

FORMER ARKANSAS GOV. MIKE HUCKABEE

High notes: A winning sense of humor and an independent streak on taxes, immigration. Off key: No international experience, little money, slip-ups in office barely examined. Stage presence: With his modest, just-folks demeanor, the most natural common touch of any candidate in either party.

ARIZONA SEN. JOHN MCCAIN

High notes: Unquestioned stature, deep international experience. Off key: Still hasn't recaptured the spark and buzz of early 2000. Stage presence: After months in the doldrums as his campaign foundered, he has recaptured his old enthusiasm.

FORMER MASSACHUSETTS GOV. MITT ROMNEY

High notes: Brandishes his wide-ranging management successes, argues he's the GOP candidate who can win blue states. Off key: Has transparently switched positions on a raft of social issues. Stage presence: The archetypal image of a successful TV pol, dogged by doubts about the depth of his core convictions.

FORMER TENNESSEE SEN. FRED THOMPSON

High notes: Seen as telegenically "presidential" in the wake of his long acting career. Off key: Started late and dramatically failed to fulfill expectations. Stage presence: Has been a lackadaisical campaigner, unable to catch fire with voters.


THE BACKUP SINGERS

These candidates mostly lack significant money and poll support:

DELAWARE SEN. JOE BIDEN (D): DEEP, LONG CONGRESSIONAL EXPERIENCE; CONNECTICUT SEN. CHRISTOPHER DODD (D): ANOTHER CONGRESSIONAL VETERAN WITHOUT SIGNATURE ISSUES; FORMER ALASKA SEN. MIKE GRAVEL (D): IF YOU UNDERSTAND HIS CANDIDACY, LET US KNOW; CALIFORNIA REP. DUNCAN HUNTER (R): A VANITY CANDIDATE WITHOUT AN ORGANIZATION; OHIO REP. DENNIS KUCINICH (D): LOUDLY, CONSISTENTLY ANTIWAR; TEXAS REP. RON PAUL (R): LIBERTARIAN, ANTIWAR WITH SURPRISINGLY LARGE BUCKETS OF MONEY GENERATED VIA THE INTERNET; NEW MEXICO GOV. BILL RICHARDSON (D): AN IMPRESSIVELY DEEP RÉSUMÉ HAS GIVEN HIM LITTLE TRACTION.