Who is he? Former venture capitalist who served one term as governor of the solidly Republican state of Virginia.
What's going to stand in his way? Mr Warner is not yet nationally known, and his four years as governor of Virginia - which limits its governors to one term - do not constitute a wealth of experience, particularly in foreign affairs or security. He can come across as physically ill at ease.
Did you know? His venture capital firm provided the initial backing for the communications firm Nextel - the success of which made an already wealthy man extremely rich.
Who is he? Rock-solid conservative senator from Virginia, a state he governed from 1994 to 1998.
What's going to stand in his way? The New Republic magazine ran a lengthy profile of Sen Allen in May 2006 alleging that he was all but obsessed as a young man with the Confederate flag - a still-controversial symbol which many Americans associate with racism. He is also facing a tougher-than-expected re-election campaign, distracting him from national ambitions at a time when opponents are laying the groundwork for White House bids.
Did you know? Sen Allen's father was a legendary American football coach also named George Allen, and his son often incorporates sports metaphors into his speeches.
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I honestly think that's race right there