A recent ABC News/Washington Post poll found if John McCain were to pick a running mate who favors legal abortion, it could cost him votes, particularly in some core Republican groups.
Among current McCain supporters, 20 percent said they'd be less likely to vote for McCain if he picked a candidate for vice president who favors abortion rights.
A Lieberman pick may have also had implications at the Republican National Convention next week. Party rules make it difficult, if not impossible, for a member of another party to be nominated on their national ticket.
Romney's stock in the veepstakes rose and fell several times in the months since he abandoned his own presidential bid. McCain and Romney sparred frequently and often personally on the campaign trail but seemed to make peace over the past few months with Romney becoming one of McCain's strongest advocates.
Nonetheless, it is Palin, a former two term mayor of Wasilla, Alaska, and two term member of the city council who joined McCain on the Republican ticket.
Sen. McCain turned 72 on Friday. The only gift he may be looking for from his new vice president? Conservative votes, independent appeal, and reach out to women who may be intrigued by the historic nature of her pick.
ABC News' Ron Claiborne, Bret Hovel, and Jake Tapper contributed to this report.