Jeff Berman, who ran Obama's delegate operation in 2008, said lobbying for the RNC delegates can be intense.
"Romney likely is telling the Republican superdelegates that he's going to be the nominee, get on board now and he'll always remember you were there when he needed you," said Berman, who recently wrote a book about Obama's 2008 campaign, titled "The Magic Number."
Santorum and Gingrich "more likely are saying vote for the candidate who is a strong conservative, who won your state and who will help get your base voters out in November to support your local candidates on the ballot," Berman said. "This may be an effective pitch in those parts of the country where Romney is struggling."
Romney's campaign made a public pitch this week that he is the inevitable nominee, calling Super Tuesday "our opponents' last stand."
Santorum has been trying to marginalize Gingrich, saying it's a two-man race and he's the man to solidify the anti-Romney vote.
Errol Galt, an RNC member from Montana who endorsed Romney on Tuesday, said he would like to see a quick end to the nomination battle.
"But this is the process we are in," Galt said. "It is going to take a lot of money if the primary is drawn out further."
Associated Press writers Brian Bakst in St. Paul, Minn., Emily Wagster Pettus in Jackson, Miss., Sean Murphy in Oklahoma City and Matt Gouras in Helena, Mont., contributed to this report.
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