Romney sets sights on Obama after Illinois win

White House hopeful Mitt Romney set his sights squarely on President Barack Obama after racking up another victory in the plodding Republican nominating race.

Romney's decisive win in Illinois Tuesday likely won't help him win Obama's home state in the November 6 election, but it has brought him closer to clinching the Republican nod.

He used his victory speech to attack Obama's economic policies and cast the November 6 general election as a choice between "economic freedom" and "job-killing regulation."

"Over the past three years this administration has been engaged in an all-out assault on our freedom," Romney told supporters gathered in an affluent Chicago suburb.

"It's time to say these words. This word. Enough. We've had enough."

Underdog Rick Santorum was unbowed by Romney's widening lead, telling supporters in his home state of Pennsylvania "we'll close this gap and on to victory!"

His campaign vowed earlier Tuesday to take the fight all the way to the Republican convention in August, but it's not clear if Santorum will be able to stop Romney from winning the 1,144 delegates needed to clinch the deal before then.

The former Massachusetts governor already had a commanding delegate lead and Tuesday's resounding win in this midwestern state will provide Romney with momentum ahead of contests in Wisconsin, Maryland and Washington, DC on April 3.

It will also provide Romney with a cushion ahead of a projected Santorum victory in Louisiana Saturday.

But with many states awarding delegates proportionally, it could take Romney until May or June to reach the majority needed to knock his rivals out of the race.

"The question isn't who's the nominee," said Larry Sabato, director of the University of Virginia's Centre for Politics. "It's whether Romney soars or limps into (the convention in) Tampa. That's not determined yet."

While Romney may have a better chance of winning over moderates and independents crucial to winning a general election, he has been weakened by his failure to win over the Republican party's conservative base in the grueling state-by-state primary race.

Written off in the early days, Santorum, a former Pennsylvania senator, has steadily notched up wins -- 10 out of 33 contests -- largely with the help of evangelicals and the party's most conservative members.

Romney's campaign spent millions flooding the Illinois airwaves with negative ads calling Santorum an "economic lightweight" and "Washington insider" who has voted against his principles in the past.

Santorum's campaign fought back by painting Romney as a man with "no core principles" who "will say and do anything for votes" and insisted Republicans could only beat Obama in November if they elect a "true conservative."

Prior to the Illinois vote Romney has pocketed 516 delegates, while Santorum has won 236 and former house speaker Newt Gingrich has 141, according to the website Real Clear Politics.

Texas Congressman Ron Paul, a small-government champion, has about 66.

Santorum's campaign has been urging Gingrich -- who has only won two contests -- to drop out of the race in order to consolidate the conservative vote.

Illinois' 56 delegates will be awarded after final results are officially tallied.

Romney had 47.5 percent of the vote with 82 percent of precincts reporting late Tuesday while Santorum had 35.2 percent, Paul had 9.3 percent and Gingrich had eight percent.