Tonight may be the last chance for Rick Santorum or Newt Gingrich to stop Mitt Romney from becoming the Republican presidential nominee. Senator Chuck Grassley hinted to The Hill today that he may endorse Romney if Romney wins the Ohio primary. I’m guessing that Newt will pull enough votes in Ohio to keep Santorum from beating Romney. I also suspect that Santorum will lose the Catholic vote in Ohio, like he did in Michigan. He and Gingrich have to hope that convincing victories in southern states give them an excuse to stay in the race.

I’ll post results from all the Super Tuesday states after the jump. Any comments about the presidential campaign are welcome in this thread.

8 pm update: Romney easily won the Massachusetts primary. So far returns show Romney at 72 percent of the vote, followed by Santorum at 12 percent, Ron Paul at 9 percent and Gingrich at 5 percent.

Romney won the Virginia primary, where Gingrich and Santorum failed to qualify for the ballot. However, he received only 59 percent of the vote compared to 41 percent for Paul, the lone “not Romney” option. (Virginia doesn’t allow write-ins for primaries.)

Early returns show a comfortable victory for Romney in Vermont, with 40 percent of the vote and Paul in second place at 26 percent, followed by Santorum (23 percent) and Gingrich (8 percent).

Gingrich won his home state of Georgia. The main question is whether he’ll hit 50 percent there, which would give him an extra 31 at-large delegates from the state. He isn’t doing better than third place anywhere else so far, although he has a chance to finish second in Oklahoma.

Santorum has won Tennessee, probably by a double-digit margin. With 25 percent of the votes counted, it’s Santorum 42 percent, Romney 28 percent, Gingrich 19 percent and Paul 8 percent. Santorum’s ahead in Oklahoma as well.

It’s still too close to call in Ohio, the big prize of the night. With 18 percent of the votes counted, Romney has 38 percent of the vote and Santorum 37 percent. Romney has to be grateful Gingrich hasn’t dropped out yet–he is pulling 15 percent in Ohio.

North Dakota, Alaska and Idaho haven’t reported any results yet.

LATER UPDATE: Romney barely managed a win in Ohio with 38 percent to Santorum’s 37 percent. Gingrich stayed at 15 percent, and Paul won 9 percent of the Ohio votes. Here are the other final preliminary results.

Romney victories

Massachusetts: Romney 72 percent, Santorum 12 percent, Paul 10 percent, Gingrich 5 percent

Virginia: Romney 60 percent, Paul 40 percent. Paul’s strong showing in a state with a heavy military presence shows how much conservatives dislike Romney. It’s also worth noting that Romney received fewer votes than either the 2008 Virginia primary winner (John McCain) or runner-up (Mike Huckabee).

Idaho: Romney 62 percent, Santorum 18 percent, Paul 18 percent, Gingrich 2 percent

Alaska: Romney 32 percent, Santorum 29 percent, Paul 24 percent, Gingrich 14 percent

Vermont: Romney 40 percent, Paul 25 percent, Santorum 24 percent, Gingrich 8 percent

Santorum victories

North Dakota: Santorum 40 percent, Paul 28 percent, Romney 24 percent, Gingrich 8 percent

Oklahoma: Santorum 34 percent, Romney 28 percent, Gingrich 27 percent, Paul 10 percent

Tennessee: Santorum 37 percent, Romney 28 percent, Gingrich 24 percent, Paul 9 percent

Gingrich victory

Georgia: Gingrich 47 percent, Romney 26 percent, Santorum 20 percent, Paul 6 percent

It’s time for Gingrich and his billionaire super-PAC funder to throw in the towel. Maybe he could have done well if he’d been on the ballot there, but he just isn’t in a position to win any remaining primary or caucus on the calendar. All he can do is keep Santorum from beating Romney.

Santorum vowed last night that he’s in the race to stay.

He argued his performance in Ohio was impressive considering how he was outspent by Mitt Romney.

During his speech, Santorum returned to his attacks on Romney, portraying the former Massachusetts governor as a weak opponent against President Barack Obama on the issue of health care reform.

“I’ve never passed a statewide government-run health care system when I was governor, because, well, I wasn’t governor. But Gov. Romney did,” Santorum said.

Santorum then referred to recent news reports indicating Romney had voiced some support for a national insurance mandate during the debate over health care reform in Washington.

“We need a person running against President Obama who is right on the issues and truthful with the American public,” Santorum said.

Romney seemed to acknowledge that winning the nomination will take a while:

“Tomorrow we wake up and we start again,” Romney told a supportive audience in Boston. “And the next day we do the same. And so it will go, day by day, step by step, door to door, heart to heart.”

By the end, Romney said, he expected to become the GOP nominee.

THIRD UPDATE: Newt Gingrich’s election night speech was something else. He’s still talking about his seven planned Lincoln-Douglas debates with President Obama, oblivious to the fact that Republican primary voters are rejecting him in most states. Click here for the full transcript and video. I expect this bit will end up on the Daily Show, Colbert Report and/or Saturday Night Live: “There are lots of bunny rabbits that run through. I am the tortoise. I just take one step at a time.”