Check out the results of the new Iowa poll, conducted by Research 2000 for KCCI-TV from December 18 through December 20:

Democrats
John Edwards 22%
Barack Obama 22%
Tom Vilsack 12%
Hillary Clinton 10%
Al Gore 7%
John Kerry 5%
Wesley Clark 4%
Dennis Kucinich 4%
Joe Biden 1%
Evan Bayh 1%
Bill Richardson 1%
Undecided 11%

Republicans
John McCain 27%
Rudy Giuliani 26%
Mitt Romney 9%
Newt Gingrich 7%
Condi Rice 4%
George Pataki 1%
Jeb Bush 1%
George Allen 1%
Sam Brownback 1%
Rick Santorum 1%
Duncan Hunter 0%
Undecided 22%

Hypothetical matchups among all survey respondents are as follows:

Obama 42, McCain 39
Obama 43, Giuliani 38
Obama 43, Romney 28

Edwards 42, McCain 39
Edwards 42, Giuliani 38
Edwards 41, Romney 29

McCain 43, Clinton 37
McCain 43, Kerry 38
McCain 41, Gore 39

Giuliani 39, Clinton 35
Giuliani 38, Kerry 34
Giuliani 36, Gore 34

Vilsack 41, McCain 35
Vilsack 42, Giuliani 35
Vilsack 45, Romney 28

Clinton 40, Romney 30
Kerry 33, Romney 30
Gore 34, Romney 28

Summarizing these results: Obama, Edwards and Vilsack beat every Republican. Hillary loses to every Republican but Romney. Romney loses to every Democrat. McCain runs slightly better than Giuliani matching up against most of the Dem field.

This poll looks like Hillary Clinton's worst nightmare in that it clearly reinforces the biggest knock against her which is that she can't win the general election.