Interviews with Republicans and legal experts today shed light on how the process could play out. At any point before tomorrow night, McCain could simply replace Palin. But once she formally accepts her nomination, he’ll no longer have the power to do so unilaterally. According to Ben Ginsberg, the former general council at the Republican National Committee, Republican rules stipulate that the 168 members of the national committee would need to ratify any replacement to make it official. The process falls under Republican Rule Number 9(a): “The Republican National Committee is hereby authorized and empowered to fill any and all vacancies which may occur by reason of death, declination, or otherwise of the Republican candidate for President of the United States or the Republican candidate for Vice President of the United States, as nominated by the national convention, or the Republican National Committee may reconvene the national convention for the purpose of filling any such vacancies.”

Ginsberg hastened to add that such a vote would almost certainly be a formality. “The members of the Republican national committee would be overwhelmingly inclined to follow the wishes of the nominee in any situation in which this rule got invoked, unless it were someone completely outside the mainstream of the Republican Party,” he said. With their experience in the national spotlight, Mitt Romney and Tim Pawlenty would be two obvious replacements. One possibility that might provoke opposition would be a pro-choice candidate, such as Democratic Sen. Joe Lieberman, reportedly on McCain’s short list until the prospect of a floor fight with conservative delegates convinced him to select Palin.

Further controversy could arise if multiple nominations were submitted. The rules state that a majority of votes is required to win the VP nod, but do not stipulate how a replacement would be chosen if a vote split among multiple nominees failed to produce a majority. “There would still be some details to fill in,” Ginsberg acknowledged.

The history of Missouri Senator Eagleton’s selection in 1972 and the 18 days he spent as George McGovern’s running mate has some striking parallels to the current campaign—and not all of them to Palin.

Just as Palin is reported to have been, Eagleton was a last-minute selection and not the candidate’s first choice. “At the 1972 convention, McGovern was facing a battle to hold onto the California delegation,” says Joel K. Goldstein, a law professor at St. Louis University School of Law and expert on the vice presidency who co-taught a course with Eagleton. “It wasn’t clear until the second or third day that he would keep California and be nominated, so it wasn’t until late in day three that he started focusing on the vice presidency.” Eagleton asked Ted Kennedy, who declined, as did Walter Mondale, Abe Ribicoff, Gaylord Nelson, and several others. “Like Palin, Eagleton had been mentioned, but was considered such an unlikely choice that he went to the convention without his press secretary. The McGovern camp had picked up rumors of possible health issues, but they never went to Eagleton and asked. Instead, they approached reporters from St. Louis papers—the local media—and asked them. There was really no serious vetting process.”