By PHILIP ELLIOTT and BEN FOX, The Associated Press
Mitt Romney took a commanding lead Sunday in early voting returns as Puerto Rico weighed in on the fight for the Republican presidential nomination. He and his chief rival, Rick Santorum, however, were nowhere to be found on the Caribbean island, campaigning instead in Illinois and Louisiana ahead of primaries in those states this week.
The race was all but certain to continue, regardless of the outcome of the trio of contests.
As the day began, Santorum claimed he was in contest for the long haul because Romney is a weak front-runner even though he comfortably leads in the fight for delegates to the nominating convention.
"This is a primary process where somebody had a huge advantage, huge money advantage, huge advantage of establishment support and he hasn't been able to close the deal and even come close to closing the deal," Santorum said of Romney. "That tells you that there's a real flaw there."
Yet, Santorum sidestepped when asked if he would fight the front-runner on the convention floor if he failed before the August gathering in Tampa, Fla., to stop Romney from getting the 1,144 needed to clinch the nomination.
Romney, in turn, expressed confidence that he'd prevail.
"I can't tell you exactly how the process is going to work," Romney said. "But I bet I'm going to become the nominee."
Both candidates campaigned on the mainland - Romney in Illinois and Santorum in Louisiana - as Puerto Rico determined who would get its 20 delegates.
With 4 percent of the precincts counted, Romney had 3,608 votes - or 87 percent - and Santorum had 311 - or 7 percent. A candidate needed to win 50 percent of the vote to claim all of the delegates; otherwise, they would be divided proportionally as long as a hopeful got 15 percent of the vote.
Both Santorum and Romney campaigned on the island last week.
In Puerto Rico, turnout appeared light and officials predicted about 150,000 people would cast ballots in primary.
Among them was Francisco Rodriguez, a 76-year-old architect who was supporting Romney, in part because the former Massachusetts governor had secured the endorsement of Gov. Luis Fortuno and other leading politicians.
"He has a stronger connection to Puerto Rico and that will help us in the process of becoming a state," Rodriguez said.
He had kind words for Santorum, describing him as a "person of faith, a good Catholic." But he said he thinks the former senator hurt himself with his statements that English would have to be the official language if the U.S. territory were to seek statehood.
"In Puerto Rico, we get along fine with both languages," Rodriguez said.
Before Puerto Rico's vote was in, Romney had 501 delegates in his camp and Santorum had 253, according to The Associated Press' tally. Former House Speaker Newt Gingrich trailed with 136 delegates and Texas Rep. Ron Paul had 50.
At this rate, Romney is on pace to capture the nomination in June unless Santorum or 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.
Even as Santorum declined to commit to forcing a brokered convention, his advisers were working behind the scenes on a plan to persuade convention delegates to switch candidates if the former Pennsylvania senator fails to derail Romney before that.
Romney's aides call this a fantasy scenario even as they try to prevent delegates from defecting.
Half of the states have yet to weigh in on a race with seemingly no end in sight anytime soon. That's prompted fresh speculation within the GOP over whether a contested convention is likely.
Republican National Chairman Reince Priebus insisted that his party will have a nominee sooner rather than later.
"We're only at halftime," Priebus said. "I think that this process is going to play itself out. We will have a nominee, I think, fairly soon - one, two months away."
As Puerto Rico voted, upcoming contests in Illinois and Louisiana loomed large, with Romney and Santorum appearing on national TV news programs and with voters. They traded barbs from afar.
"Sen. Santorum has the same economic lightweight background the president has," Romney told a crowd in Moline, Ill. He went a step further in Rockford, Ill., saying, "We're not going to replace an economic lightweight with another economic lightweight."
That drew a Santorum retort: "If Mitt Romney's an economic heavyweight, we're in trouble."
Aside from a pair of TV interviews, Santorum spent the day visiting a pair of churches in Louisiana, sharing how his faith has shaped his political career and his opposition to abortion rights and gay marriage. He didn't mention Romney or any of his other Republican opponents during talks at both churches.
He made clear he didn't plan to exit the race anytime soon, saying in Bossier City, La., "One of the great blessings I've had in every political campaign is people underestimate me, people underestimate what God can do."
Yet, he was curt when asked about his odds in Illinois.
"Keep working," Santorum said after services there. "That's all we can do."
Santorum spoke with CNN's "State of the Union" and ABC's "This Week." Romney appeared on "Fox News Sunday," and Priebus was interviewed on CBS' "Face the Nation."
Associated Press writers Andrew DeMillo in Bossier City, La., and Kasie Hunt and Ben Fox in San Juan, Puerto Rico, contributed to this report.