For Newt Gingrich, staying in the presidential race grows more and more difficult with each passing primary he doesn’t win.

That didn’t stop him from pledging to fight on despite losses to Rick Santorum on Tuesday in Alabama and Mississippi — Southern states that Gingrich and many Republicans have said he had to win to remain viable after a string of defeats this year.

Less clear is whether it’s possible for Gingrich to attract the support — and dollars — he needs to continue. Yet there may not be anyone who can compel him to drop out. His rationale for staying in the nominating contest is less and less about a path to victory — and increasingly driven by a defiant rejection that Mitt Romney is best suited to challenge President Obama in the fall.

The closeness of the three-way competitions in Alabama and Mississippi underscored the dynamic among Gingrich, Romney and Santorum. Gingrich told an Alabama radio show Tuesday that a “tag-team” approach with Santorum would deny Romney the delegates he needs for the nomination.

“We are going to leave Alabama and Mississippi with a substantial number of delegates, increasing our total as we head toward Tampa,” Gingrich told a small but enthusiastic crowd Tuesday night in Birmingham. “I emphasize ‘going to Tampa’ because one of the things tonight proved is that the elite media’s effort to convince the nation that Mitt Romney is inevitable just collapsed. The fact is, in both states, the conservative candidates got nearly 70 percent of the vote.”

If Gingrich does continue, there may be an unlikely beneficiary: Romney, the Republican front-runner. After months of contentious, sometimes bitter campaigning against each other, Gingrich’s determination to remain a candidate until the Republican National Convention in August allows Romney to avoid what some in the GOP see as a bigger threat: a one-on-one confrontation with Santorum.

Gingrich is also helping the party generally, many Republicans said, by pushing issues that resonate with GOP voters — notably the high price of gas, a topic the former House speaker mentions at every stop and in nearly every TV interview. His success in rallying Republicans with such battle cries could help whoever becomes the nominee face Obama in the fall.

“Newt has claimed a lot of territory for the Republicans on the energy issue — and it’s not just the last few weeks,” said Vin Weber, a Romney supporter and former congressional colleague of Gingrich’s. “He’s the guy who went through the last campaign in 2008 saying, ‘Drill, baby, drill.’ In no small measure we own that issue today because of Newt, so I give him a lot of credit for that.”

On everyone’s mind, however, are these questions: At what point does Gingrich’s extended struggle to regain momentum on the campaign trail start to hurt Republicans? And at what point does it hurt him? Over the course of this campaign, Gingrich has reestablished himself as a leading voice of ideas within the GOP. The last thing he and his supporters want is for the 68-year-old to exit the presidential race, and perhaps the public stage, as the Ralph Nader — the stubborn spoiler — of the party.

Saul Anuzis, a key Romney supporter and a former chairman of the Michigan Republican Party, said Gingrich needs to abandon the race soon. But for now, he is helping the party by galvanizing Republicans against Obama.

“If nothing else, Newt is a historian,” Anuzis said, “and he realizes either he’s going to be an upset victor, a gracious loser or a spoiler — and that’s how history will view him. This is kind of his last hurrah, and he realizes that as much or more than anyone else. I am one who does not believe that he is just going to crash and burn and go down with the sinking ship. I think he’s going to be a team player and do the right thing. It’s just not going to be today.”

Indeed, the Gingrich campaign announced plans Tuesday to head to Illinois and Louisiana this week, with the possibility of trips to Texas and Wisconsin after that. Gingrich spokesman R.C. Hammond said the candidate has his sights set on contests in those states as well as the California primary in June. Hammond also said the campaign is planning a “floor whip operation” for the convention in Tampa.

In addition, the campaign issued an internal strategy memo declaring that it is merely halftime in the nominating contest, which won’t be won and lost “until the fourth quarter” — after a long slog of additional contests across the nation, including more Southern states, where Gingrich is strong, as well as Wisconsin, home state of his wife, Callista Gingrich.

“When we’re done with this, after Texas, where I think I’ll do very, very well, and California, which is the last big state to vote, we’re going to run a 60-day discussion, and people are going to have to look at who could really beat Barack Obama,” Gingrich said on Fox News early Tuesday. “And I think that will be a very — it will be historically for you guys — the most interesting possible process leading up to a real convention. “

The greatest concern for Romney’s camp as it looks ahead to a nomination battle with no end in sight is a smaller and smaller window in which to turn its main focus to Obama and build a strong fall campaign.

“I don’t necessarily buy the notion that all the negativity is destroying our candidates,” Weber said. “There’s simply not enough time. It’s a question of organizing a national campaign. It takes time to organize a campaign . . . draw up a strategy and advertising campaign. You need to turn your attention at some point to defeating the incumbent in the White House.”

Early in the day, Alabama GOP Chairman Bill Armistead predicted in a CNN interview that Gingrich losses in Mississippi and Alabama would mean “he’s out of the ballgame.”

Still, those calls could be muted because so many Romney allies now see Gingrich — whom Romney and his allies targeted just a few weeks ago in Iowa and Florida with millions of dollars in negative ads — as a barricade against Santorum, the former senator from Pennsylvania. Romney, the former Massachusetts governor, has trained his firepower far more directly on Santorum in recent weeks, and he only narrowly defeated him in two key states, Michigan and Ohio. With Gingrich gone and no longer competing with Santorum for the party’s more conservative voters, such close contests could grow even more challenging for Romney.

And so could the challenge to excite GOP voters. Gingrich has campaigned heavily on the issue of energy independence, generating large crowds and big cheers with a pledge to increase oil exploration and a promise to reduce the price of gas below $2.50 a gallon.

“Barack Obama is responsible for the high price of gasoline,” Gingrich said in an interview on Fox News early Tuesday. “He has followed a deliberately anti-American energy policy.”

“Clearly Newt is one of the best messengers our party has, so having him raise the issues — few people do it more effectively than he does,” Anuzis said. “From that standpoint, it’s a good thing that he’s in.”