Mitt Romney campaigns in Illinois
He also accused Romney of forcing Catholic hospitals to provide the morning-after pill when he was governor. Santorum argued that the pill "caused abortion."
As a gubernatorial candidate in 2002, Romney signed a Planned Parenthood questionnaire that he supported using state tax dollars to fund abortion services through Medicaid for low-income women, according to a copy of the questionnaire.
He also pledged support for increased access to emergency contraception such as the "morning-after pill," which he now condemns as an "abortive pill." Santorum said that he'll "go out and compete in every state," calling Illinois a "two-person race."
"What I've said is, I think it's going to be very difficult as this goes on for anybody to get that magic number" to clinch the nomination, Santorum said in an interview on CBS's "This Morning."
Santorum called Romney a "big-government heavyweight," responding on MSNBC Monday to the former Massachusetts governor's recent assertion that he couldn't match up on economic expertise.
Santorum told CBS he thinks the chances of a brokered GOP convention in August "are increasing."
In nationally broadcast remarks Sunday, Santorum sidestepped when asked if he would fight Romney on the convention floor if he failed before August to stop the former Massachusetts governor from getting the required number of delegates.
Romney aides privately likened the situation to the Black Knight in "Monty Python and the Holy Grail" who loses his arms and legs in battle with King Arthur but insists he has only a flesh wound.
The Romney camp suggested that Tuesday's performance would extend Romney's delegate advantage, even if he loses the popular vote. Santorum cannot win at least 10 of the state's 54 delegates because his campaign failed to file the paperwork.
Polls suggest a Romney edge in Illinois. At a Romney campaign stop Sunday, voters were divided.
"I'm leaning toward Santorum, but I wanted to hear him in person," said Nichole Warren, a 32-year-old stay-at-home mom from nearby South Beloit. "I hear (Romney) talk and I hear a lot of Obama in him, and that scares me."
But Sid Haffenden, a 61-year-old retired toll-way worker, said, "Santorum has too much baggage." He added, "I want a businessman."
At this rate, Romney is on pace to capture the nomination in June unless Santorum or former House Speaker Newt Gingrich is able to win decisively in the coming contests.
Both have said they would stay in the race and perhaps force the nomination to a fight at the GOP's convention in Tampa if Romney doesn't amass enough delegates to arrive with a mandate.
That would turn the convention into an intra-party brawl for the first time since 1976. Including Puerto Rico's results, Romney has now collected 521 delegates, compared to Santorum's 253, Gingrich's 136 and Paul's 50, according to The Associated Press count.
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