Image credit: Eric Gay/AP Photo

Rick Santorum's top opponent in Iowa is Mitt Romney and the biggest argument against a President Romney is health care, the former Pennsylvania senator told me.

"This has been a debate about health care, that's what the behemoth of government, the signature issue is Obamacare.  We cannot put up a presidential candidate who is in basically in the same place as Obama on government-run health care" Santorum said on "GMA."

He acknowledged that he supported Romney in 2008 but said there was only "one question" about health care in a debate four years ago. This year it's one of the biggest issues. 

The latest Des Moines register poll showed that Santorum is gaining momentum heading into the caucuses and he told me he's confident he'll "do very well tonight."

The former Senator spent the majority of his campaign in the Hawkeye state, held hundreds of town hall meetings and visited all 99 counties. But if he wins tonight he'll be up against a well funded Romney in New Hampshire, who has raised more than $32 million compared to Santorum's $1.2 million.

 Santorum admitted low fundraising, telling me "I would say we've done this on shoestring but that would be insulting shoestrings."  But he was optimistic tonight's results will help. 

"We feel very, very good that we've got the organization and money is coming in better than it's ever come in and when we do well tonight we suspect we'll have the resources to be able - not just to compete in New Hampshire but to compete all the way thru," Santorum said.

He hopes to face the president in the general election and has been aggressive criticizing Obama on national security. Yesterday he attacked Obama for siding "with our enemies on almost every single" foreign conflict, according to the Washington Post, despite taking out Osama bin Laden and other top al Qaeda leadership.

"That was a mission that was already decided. That was U.S. policy to kill Osama Bin Laden and to kill al-Qaeda and to treat them as enemy combatants. The president did not change that policy, but that was not a policy or problem that came up under his watch," Santorum said on "GMA." "The ones that did come up under his watch - Iran, Egypt, Syria, Honduras, you can go on down the list, Poland, the UK, the Czechs,- ask all of them - Israel - whether we've been a good ally, one that you can stand by and look at the ones who have been enemies of the United States, and we have appeased and pandered. This is a president that has gotten it wrong when every time there has been a decision to be made when it is in the interest of the United States, when a contingency came up under his watch, he's blown it."

Watch my interview here: