Romney hopes to bag Wisconsin in a primary hat-trick

Mitt Romney is aiming for a triple primary victory as voters in Wisconsin, Maryland and Washington DC pick a Republican presidential candidate.

The former Massachusetts governor is hoping to knock main rival Rick Santorum out of the race so he can sew up his party's nomination.

Opinion polls suggest Mr Romney is leading in Wisconsin and Maryland.

But Mr Santorum does not seem ready to bow out of the race to become the challenger to President Barack Obama.

If Mr Romney cannot score a decisive blow against Mr Santorum on Tuesday, he will try to do so in the former senator's home state of Pennsylvania, which holds its primary on 24 April.

As of Monday, Mr Romney had 568 of the 1,144 delegates needed to clinch the Republican nomination at the party's convention in August, according to an Associated Press tally.

Mr Santorum was far behind with 273 delegates, while Newt Gingrich had 135 and Ron Paul 50.

Mr Romney's campaign was given a boost last week in the Midwestern state of Wisconsin by an endorsement from local congressman and budget committee chairman Paul Ryan.

Mr Romney, a former Massachusetts governor, campaigned with Mr Ryan on Monday in Green Bay, Wisconsin, at a building supply company.

"We're looking like we're going to win this thing," said Mr Romney a day earlier.

But Mr Santorum was sounding optimistic about his chances in Wisconsin, Tuesday's most important primary, where the race was closest between the two candidates.

"We're going to have a good result here in Wisconsin," the former Pennsylvania senator told Fox News on Monday. "Maybe even sneak in and have an upset."

The social conservative said his campaign had been successful even in the face of Mr Romney's "overwhelming money and overwhelming establishment support".

On Monday, Mr Romney all but ignored his Republican rivals to attack Democratic President Obama, accusing him of "crushing dreams" with a "government-centered society".

"He takes his political inspiration from the capitals of Europe," Mr Romney told supporters in Green Bay.

But the three-month long primary battle has left the Romney campaign looking for new ways to raise money ahead of an anticipated race for November's general election.

While the former Massachusetts governor is well-funded among his Republican rivals, he is already lagging behind Mr Obama.

The Obama campaign has $87m (£54m) on hand as of the end of February, compared with Mr Romney's $7.3m. The Obama campaign has more than 530 paid staff while Mr Romney's has about 100.

Mr Romney and his allies have already spent $53m in advertising during the primary season, almost twice the rest of his Republican rivals combined.

A new Gallup poll also suggested that Mr Obama was leading Mr Romney slightly in a potential general election match-up, including in key swing states.