Good news -- Democrats have a winner:

Obama Leads Four Republicans in U.S. Race

Democrat Barack Obama is the top 2008 presidential contender in the United States, according to a poll by Zogby International. At least 46 per cent of respondents would support the Illinois senator in head-to-head contests against four prospective Republican nominees.

Obama holds a three-point edge over Arizona senator John McCain, a six-point lead over former New York City mayor Rudy Giuliani, and a 17-point advantage over both former Massachusetts governor Mitt Romney and actor and former Tennessee senator Fred Thompson....

Too bad he's losing badly in his own party in key states:

A new batch of American Research Group polls give the edge to Sen. Hillary Clinton in all three early states of the 2008 presidential race. Sen. Barack Obama has slipped to third place behind John Edwards in each state, while Bill Richardson is up in Iowa and New Hampshire.

Iowa: Clinton 35%, Edwards 25%, Obama 11%, Richardson 8%
New Hampshire: Clinton 34%, Edwards 18%, Obama 15%, Richardson 9%
South Carolina: Clinton 34%, Edwards 18%, Obama 11%

Ah, but the good news is that the somewhat weaker McCain, not Giuliani, is leading in those key-state ARG polls:

Iowa: McCain 25%, Giuliani 23%, Romney 16%
New Hampshire: McCain 30%, Romney 23%, Giuliani 21%
South Carolina: McCain 32%, Giuliani 23%, Thompson 13%,

But the bad news is that, in the Zogby poll, McCain beats Clinton 47%-43%. (She also loses to Giuliani, and she has only an 8-point lead over Romney, as compared to Obama's and Edwards's double-digit leads.)

So why do we Democrats seem almost certain to nominate our weakest top-tier candidate? And (as I'm always saying) if the unpopularity of the war is such a millstone for every Republican, why is any Republican beating any Democrat?

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UPDATE WEDNESDAY: My response to the Politoco's story on Thompson's entry into the race is here. Short version: I think it might help McCain.