(CBS News) CHICAGO - Mitt Romney won the Illinois Republican primary by a huge margin Tuesday, and Rick Santorum slipped further behind in the delegate count.
Romney won 47 percent of the vote in Illinois. Santorum was a distant second with 35 percent, followed by Ron Paul and Newt Gingrich in single digits.
Romney's decisive victory strengthens his argument that he's going to be the nominee, and that the other candidates should get on board so they can stop fighting each other and instead focus their energy on President Obama.
Romney lost with evangelicals and the very conservative, but won in almost all other groups -- and picked up ground where he's struggled. In Illinois, he was seen as the candidate who best understands voters' problems. And he won overwhelmingly among voters who care most about beating Mr. Obama.
"We know what President Obama's vision is," Romney said. "We've been living it these last three years. My vision is very, very different than what his is."
But Santorum, who's already campaigning in his home state of Pennsylvania, where he predicts he'll do very well, refuses to step aside. He said over and over again Tuesday night that Romney is not what the American people are looking for.
"We don't need a manager," Santorum asserted. "We need someone who's gonna pull the government out by the roots and throw it out and do something to liberate the private sector. That's what we need."
Despite lagging far behind, Gingrich found a way to make news.
Campaigning in Louisiana, he slammed actor Robert De Niro for something he said in front of Michelle Obama during a fundraiser for the president. De Niro, who says he was joking, asked the crowd, "Do you really think our country is ready for a white first lady?"
Gingrich took issue with the comment's racial tone, saying, "What De Niro said ... was inexcusable, and the president should apologize for him. It was at an Obama fundraiser, it is exactly wrong, it divides the country."
Gingrich finished dead last here, behind Ron Paul. But, like Santorum, he's saying he's staying in this thing. He's not going to drop out -- as they both try to deny Romney the nomination. But that's going to be a lot harder after last night. Romney picked up most of the 54 delegates that were in play here, giving him 534 delegates, CBS News estimates, putting Romney almost halfway to the magic number of 1,144.
Whether the race is now over is the question everybody is asking, because it looks impossible for any of the other candidates to get to that magic number, other than Romney. So, you're hearing Romney and a lot of Republicans (Wednesday)morning saying, it's over. They're saying Santorum and Gingrich are now hurting the Republican party by continuing to beat up on Romney, which is softening some of his approval numbers with voters and hurting the party as it tries to go head-to-head with Mr. Obama in November.
But Santorum and Gingrich they're saying, 'Listen, we're not going to quick, because we don't think Romney can beat President Obama, and that's why we're staying in.' But, if you look at the delegate count, you look at the states ahead, it's hard to see how it's anything but over for those two unless something magical happens for them at that convention.
Electability is one thing issue Romney continues to poll well on. He did here on Tuesday night. He did in every state. And these republican voters want president obama out of the white house. That's what they care about. Even voters who don't say they really like Mitt Romney that much are voting for him because they think he has the organization, the money, the skills and the message to beat President Obama, more than Santorum, more than Gingrich, more than any other unnamed candidate who get somehow into the race.
To see Jan Crawford's report, click on the video in the player above.