santorum
As Mitt Romney marches toward the Republican presidential nomination, Rick Santorum is making his latest "last stand" in his home state of Pennsylvania. REUTERS

Rick Santorum and Newt Gingrich are clinging on in the Republican presidential contest, while Mitt Romney marches toward the nomination.

Both are still in the campaign, despite beingfafr behind Romney in the delegate count. Meanwhile, names are being floated as possible running mates for Romney. And even U.S. President Barack Obama is calling out the former Massachusetts governor by name, something he had never done so far this year.

Romney, too, is looking to November. He recently told a crowd in Pennsylvania he will beat Obama there, the Philadelphia Inquirer reported, never mentioning Santorum, who represented the state in the Senate for two terms.

Meanwhile, Santorum is making his home state's April 24 primary contest the campaign's latest last stand and Gingrich on Sunday conceded that Romney will most likely be the nominee. Meanwhile, Texas congressman Ron Paul, a libertarian with a small but dedicated cadre of supporters, soldiers on, having gained more votes than Gingrich in some Midwestern contests.

Home In Pennsylvania

On Tuesday, Santorum will start campaigning after going on a hiatus to care for his 3-year-old daughter Bella, who was hospitalized last week.

Fighting against the perception Santorum was about to withdraw after Romney won the Wisconsin primary last week, the senator's campaign released a schedule showing four Pennsylvania events over three days. The schedule includes a meeting with a local Republican party, prominent evangelical James Dobson of Focus on the Family, and participating in a Red Meat Tour with a local radio host.

Last week, Santorum said on CNN he needs to keep his campaign viable until the end of April. After that, the contest will be held in states such as Texas, Arkansas, Kentucky, West Virginia and North Carolina, where Santorum hopes that his social conservatism will help him win.

Those are the states that we know we can get this back, right back to where it is right now, which is a lot closer than what Mitt Romney and the pundits are spinning, he said last week on CNN's Piers Morgan Tonight.

'Far and Away' the GOP Nominee

Gingrich is continuing to slog through the primary, following a string of fourth- and third-place finishes. Yet Gingrich, a former speaker of the U.S. House of Representatives, said Sunday that Romney is far and away the GOP presidential nominee.

I think you have to be realistic, Gingrich said on Fox News. He is far and away the most likely Republican nominee and if he does get to 1,144 delegates [needed to win the nomination], I'll support him. I'll do everything I can this fall to help him beat Obama.

Gingrich, whose shoestring campaign operation is in debt, said there is a good response to his message in Delaware and North Carolina, where he campaigned Monday ahead of the latter state's May 8 primary.

Gingrich suggested he is staying in the race to influence the platform, ensuring the party's policies are sufficiently conservative and that Romney will adhere to them.

I suspect he will accept a solid conservative platform, he said of Romney, but he does have consultants who are in the Etch A Sketch tradition who would like to somehow go into the situation and not have anyone there.