Romney sweeps three primaries - FT.com Primary results (AP) State (Votes counted*) Mitt Romney Rick Santorum Newt Gingrich Ron Paul Maryland (71%) District of Columbia (67%) Not on ballot Wisconsin (82%) Updated: 11:30pm EST Mitt Romney secured solid wins in the Wisconsin, Maryland and the District of Columbia, overwhelming his opponents and piling pressure on them to quit the race for the 2012 Republican nomination. Mr Romney's sweeping victories will give him the bulk of the 98 delegates at stake in the three ballots, reinforcing an already all but an impregnable lead over Rick Santorum, his chief rival. In total, Mr Romney had accumulated at least 646 delegates to Mr Santorum's 272 after Tuesday's primaries - putting him more than halfway to the 1,144 needed for the nomination. Mr Santorum would need to win 76 per cent of all the remaining delegates in upcoming primaries to win the nomination, the Associated Press calculated - a next-to-impossible task unless Mr Romney exited the race. The fourth remaining candidate, Ron Paul, is also not in a position to threaten the former Massachusetts governor. Neither has indicated they will drop out anytime soon. After almost weekly debates, primaries and caucuses from late last year, the next three weeks contains no ballots and set pieces, making Mr Santorum's task more difficult. The five states holding primaries on April 24 include Pennsylvania, which Mr Santorum represented in the Senate until he lost his seat in a landslide in the 2006 midterm election. Mr Santorum has a slight lead in early polls there and believes the primary calendar in May, in large states like Texas, will suit him. Mr Santorum insists he is not dropping out, saying in a statement issued through his spokesman that "Pennsylvania is pivotal for our campaign, but it's also pivotal for Romney." Speaking in Mars, Pennsylvania, Mr Santorum urged his supporters to "charge out of the locker room for a strong second half" in the nomination race. Increasingly however it appears that it is a question of not if, but when he drops out and what price he attempts to extract from Mr Romney when he does so. "Mitt Romney will be the Republican nominee," said Stuart Stevens, one of Mr Romney's chief advisers, after the Wisconsin result. Mr Romney's win took place against the background of a rising partisan atmosphere, following President Barack Obama's strong attack on Tuesday on the recent budget plan passed by Republicans in the House of Representatives. The budget was drafted and shepherded through the house by Paul Ryan, the Wisconsin congressman and the chair of the house budget committee, and supported by Mr Romney. Mr Obama called the plan's cuts to aged healthcare and government programmes combined with large reductions cuts for the wealthy "thinly veiled social Darwinism" and mocked Mr Romney's description of it as a "marvellous budget." Mr Romney delivered his winning speech in the Grain House in central Milwaukee, a grandiose turn of the century building with soaring ceilings, frescoes and a bell tower. Introduced to the cheering crowd by Mr Ryan, he said that "under this president's watch, more Americans have lost their jobs than during any other period since the Depression, millions have lost their homes and a record number of Americans are living in poverty." We have a sacred duty to restore the promise of America. And we will do it. We will do it because we believe in America. Wisconsin Republican Senator Ron Johnson, who is in charge of co-ordinating Republicans on Capitol Hill with the Romney campaign, said he was certain a "comprehensive" explanation of the Ryan budget would win over voters. We can breakthrough on this. I think we have the support of the American people," he said. Both Mr Romney and Mr Santorum will be campaigning in Pennsylvania on Wednesday.