Mitt Romney wins Puerto Rico Republican primary Mitt Romney on the campaign trail at a restaurant in Rockford, Illinois. He won an overwhelming victory in the Puerto Rico GOP primary. Photograph: Steven Senne/AP Mitt Romney has won an overwhelming victory over chief rival Rick Santorum in Puerto Rico's Republican presidential primary. But Romney was campaigning far away in the critical heartland state of Illinois ahead of Tuesday's primary, which offers another chance to prove he is the inevitable Republican candidate in the extended fight for the nomination to challenge Barack Obama in the November election. The former Massachusetts governor and multimillionaire, who accumulated his fortune buying and selling troubled business ventures, has proven singularly unable to win the hearts of the base of the Republican party, an increasingly conservative bloc of voters who distrust Romney for his moderate past positions on important social issues like abortion and gay rights. As the day began, Santorum, a former Pennsylvania senator, claimed he was in the contest for the long haul because Romney is a weak frontrunner even though he comfortably leads in the fight for delegates to the nominating convention. Santorum campaigned on Sunday in the southern state of Louisiana, which holds its primary on Saturday. "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. To gain the nomination, Romney must accumulate 1,144 delegates to the Republican National Convention - allocated through state-by-state primary elections and caucuses. Romney is on course to capture the nomination in June unless Santorum or Gingrich is able to win decisively in the coming contests. Before Puerto Rico's vote was in, Romney had 501 delegates, more than all of his rivals combined. Santorum stands at 253, former House speaker Newt Gingrich has 136, and Texas Republican Ron Paul is at 50, according to an Associated Press projection. Enrique Melendez, the Republican representative on the Puerto Rican state electoral commission, said Romney would top the 50% of the vote needed to win all 20 of the island's convention delegates. Both Santorum and Romney campaigned last week in Puerto Rico, the US commonwealth island in the Caribbean island, where residents are US citizens but cannot vote in the November presidential election. Romney secured the endorsement of Puerto Rico governor Luis Fortuno and other leading politicians. Santorum hurt himself with statements that English would have to be the official language if the US territory were to seek statehood. Romney expressed confidence that he would eventually prevail. "I can't tell you exactly how the process is going to work," Romney told Fox News Sunday. But I bet I'm going to become the nominee, I sure hope I'm going to become the nominee. The importance Romney places on Illinois showed itself over the weekend when he cut short a visit to Puerto Rico and added campaign events in the Midwestern state. Romney's campaign was taking no chances in Illinois after losses to Santorum last week in the Deep South primaries in Mississippi and Alabama. Romney is favoured in Illinois after eking out victories over Santorum in Michigan and Ohio, two other industrial states in the middle of the country. Romney is likely to do best in the densely populated Chicago region in the northeastern corner of the state, but Illinois voters become increasingly conservative - and more likely to mark ballots for Santorum - across the central and southern regions. The outcome will depend upon how many Chicago-area voters abandon Romney for either Santorum or, less likely, Gingrich. The former speaker of the House of Representatives has focused his campaign in the south, but even there he finished second to Santorum in Mississippi and Alabama. Santorum wants Gingrich to leave the race, a move that would allow Santorum to consolidate the conservative opposition against Romney. Both Santorum and Gingrich have said they would stay in the race and perhaps force the nomination to a fight at the Republican convention in Tampa, Florida, 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 when Gerald Ford turned back a challenge by Ronald Reagan. Santorum hopes that a strong showing in the remaining state contests would enable him to claim a mandate and persuade delegates to ignore election results in their states and go with him as the more conservative option over Romney. But there's a hitch, and that is Gingrich's refusal to quit the race even though he has only won primaries in South Carolina and Georgia, which he represented in Congress for two decades. Romney's aides call this a fantasy scenario even as they try to prevent delegates from defecting. As Puerto Rico voted, Romney and Santorum traded barbs from afar on national TV news programmes and at campaign events. "Senator Santorum has the same economic lightweight background the president has," Romney told a crowd in Moline, Illinois. 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, Louisiana, "One of the great blessings I've had in every political campaign is people underestimate me, people underestimate what God can do."