As an introduction to our latest race rankings, here's an elaboration.

Here are some bullet points:

** Four consecutive reputable national polls show that Hillary Clinton topping 50% of the vote in a multicandidate primary. These surverys have been conducted as Democrats pay more and more attention to the candidates.

** As First Read points out this morning, it's facile to look back only to 2004 and note that Howard Dean, leading in the polls at this point, fell to John Kerry. (1) Clinton is a much better candidate with much more money; (2) her support is much stickier and more broadly distributed across the party; (3) Dean never approached 50% in these polls; (4) Clinton's campaign won't stall the way the Dean's did; (5) Dean never met the credibility test; Clinton wrote the credibility test; (6) Clinton has a natural, solid in with women, who vote out of demographic proportion in Iowa and New Hampshire.

** In the past, such as in 1984, the calendar worked to the frontrunner's advantage; Mondale was able to outlast Hart. No longer. This year, the calendar plays to the insurgent's advantage in that it is so scrunched up that a single defeat or case of expectations not being met will hurt the frontrunner. It won't kill her, but she'll need to find a firewall state in a hurry.

** In the same vein, Barack Obama is like no other challenger in history. He is not Gary Hart to Clinton's Walter Mondale. (1) He is the best-funded top-tier challenger in the history of American politics; (2) no candidate's biography better intersects with the historical moment; (3) the calendar benefits him.

** This is three-dimensional chess: Obama's frame -- Hillary's Establishment Versus A New Direction -- is and has been the frame of a credible, fairly-well-funded candidate: John Edwards, who currently polls better or equal to Obama in Iowa. And Edwards has the policy proposals to highlight his distinctions.

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