The Iowa primary is shaping up to be a nail-biter, with Mitt Romney, Ron Paul, and Rick Santorum all within two points of each other in a new poll. According to Public Policy Polling, Paul leads with 20 percent of likely caucus-goers, Romney follows with 19, and the surging Santorum finishes with 18. Romney is responding to Santorum's rise by stepping up attacks, calling him a career politician, even as his campaign downplays the significance of winning Iowa and turns toward New Hampshire, South Carolina, and Florida.