Sun partner Politico has reporters on the ground in Iowa, where the Democratic race has taken on a new dynamic, as I picked up when I was there earlier this month.

Essentially, Obama is running like a frontrunner, Clinton as a challenger.

DES MOINES — In a reversal of fortune, Sen. Barack Obama (D-Ill.) is barnstorming Iowa with a front-runner’s swagger while Sen. Hillary Rodham Clinton (D-N.Y.) scrambles like an underdog.

In ways big and small over the weekend, the two campaigns exuded a sense of switched identities — a dynamic driven by poll-driven perceptions that Clinton’s sense of inevitability is slipping and Obama is riding a bit of a wave amid the Midwestern seas of grain.

The mood and stump styles of the two campaigns reflect this new reality: An ebullient Obama — coatless, tieless, tireless — conveys a sense that at least he thinks he could be on his way to being the next president. Clinton, mixing her traditional caution with a new toughness, is clearly set on knocking Obama off his game.

The race here, where according to polls Clinton holds a big lead, will change very suddenly if Obama wins in Iowa.

On the Republican side, Rudy Giuliani is now attacking his chief challenger Mitt Romney, and specifically his record as governor of Massachusetts on crime, taxes and social issues. It was only a matter of time before they got after each other. It’s likely to get ugly. Here’s The Washington Post.