BIRMINGHAM, Alabama (Reuters) - It turns out that Newt Gingrich will not take "no" for an answer.
A day after finishing second in Republican presidential primaries in Alabama and Mississippi that he had cast as must-wins for his flailing campaign, Gingrich pressed forward on Wednesday, even as calls for him to drop out persisted.
But as Gingrich campaigned in Illinois - which on Tuesday will host the next big contest in the state-by-state fight for the Republican nomination - it was clear that many Republicans now see the race as a two-man battle between Mitt Romney and Rick Santorum.
Republican leaders and activists speculated openly about the impact of a Gingrich withdrawal, and whether conservatives who support the former U.S. House speaker would flock to Santorum and make him competitive with Romney, the Republican front-runner.
"Rick Santorum really needs Newt Gingrich to get out of the race," said unaffiliated Republican strategist Ford O'Connell. "Gingrich may only be taking 10 to 15 percent of the vote as the race goes on, but the majority of that would otherwise be going to Santorum and that makes a huge difference.
"Romney is, without a doubt, the beneficiary the longer Gingrich stays in the race. ... This race is going to keep going and going."
The battle to determine who will face Democratic President Barack Obama in the November 6 election is a hunt for votes, but more importantly it is a hunt for party delegates, whose support is awarded based on how candidates fare in primaries and caucuses. A candidate needs 1,144 party delegates to clinch the nomination.
Romney, a former Massachusetts governor who has superior funding and organization, has 484 delegates, according to CNN's estimate. Santorum, a former Pennsylvania senator, has 239, while Gingrich has 136 and Texas Congressman Ron Paul, 69.
And so, the theory goes, if Gingrich were to drop out and endorse Santorum - and if nearly all of Gingrich's delegates sided with Santorum in a unification of anti-Romney forces - Santorum would be within striking distance of the front-runner in the delegate count.
It's unclear, however, whether a huge majority of Gingrich's delegates would side with Santorum if Gingrich were to leave the race.
In exit polls in Alabama, Mississippi and several other states that have held contests this primary season, solid majorities of Republican voters have said that defeating Obama this fall is their top priority, and that they see Romney as the Republican with the best chance of doing that.
The "electability" question could drive some delegates currently committed to Gingrich to support Romney, several political analysts said.
Under Republican Party rules, "when a candidate drops out, their delegates are free to support anyone," said Kirsten Kukowski, a spokeswoman for the Republican National Committee.
Kukowski said the delegates of a candidate who leaves the race are not bound by any endorsement of the departing candidate.
With contests in Missouri (Saturday), Puerto Rico (Sunday) and Illinois (Tuesday) coming up, Romney made a pit stop at a luxury hotel in New York for the type of fuel that drives a campaign: cash.
At a fund-raiser at the Waldorf Astoria where donors paid $1,000 and up for lunch, Romney met with supporters such as Woody Johnson, owner of the New York Jets football team.
In a signal that it will spend big to try to win in Illinois, Romney's campaign directed nearly $1 million toward advertising in that state, where recent polls indicated he is clinging to a narrow lead over Santorum.
Restore Our Future, the independent "Super PAC" that supports Romney, has spent about $3.7 million to air anti-Santorum ads in Illinois, mostly in Chicago, according to a Republican media buyer who tracks advertising.
In Puerto Rico, Santorum showed a new side to his conservative platform, which has included calls for more religion in government and greater restrictions on abortion.
Santorum told a crowd in San Juan that the U.S. territory would have to make English its official language if it wanted to pursue U.S. statehood, a position that appears to conflict with the U.S. Constitution.
For Gingrich, the road ahead could be increasingly rocky.
After being topped by Santorum in Alabama and Mississippi, Gingrich faces an April schedule of contests in Romney-friendly states that could allow the former Massachusetts governor to put some distance between himself and his rivals.
Gingrich had long counted on a big boost from the conservative state of Texas, where 155 delegates will be at stake.
But a legal dispute over the redrawing of congressional districts in Texas has delayed the state's primary from April 3 to May 29. And recent polls in Texas suggest that Santorum is now favored by most Republicans there.
Santorum has run a relatively low-budget campaign throughout the primary season, but the campaign announced recently that it raised $9 million in February, as he rose in the polls.
Gingrich's financial picture is considerably more murky.
Campaign fund-raising and spending reports for February are not due to the Federal Election Commission until next week, but the Gingrich campaign spent little money on advertising in Mississippi and Alabama, even as Gingrich was saying the states were crucial to his success.
And Winning Our Future, the pro-Gingrich Super PAC that has been propped up by nearly $11 million in donations from the family of Las Vegas casino magnate Sheldon Adelson, has reduced its advertising on TV and invested in less-expensive radio ads, suggesting the PAC could be running low on money.
Adelson has not indicated whether he will pour more money into the PAC.
Rick Tyler, a former Gingrich aide and a senior adviser to Winning Our Future, acknowledged that Tuesday's results "won't make it easier for fundraising.
But all the people in our PAC are loyal and dedicated to Newt Gingrich," Tyler said.
"We're going to keep going as long as Newt Gingrich is in this race. Money makes things easier, but (a lack of it) is not going to stop us from going forward. We'll just have to work harder at making news."
Editing by David Lindsey; Desking by Eric Walsh