National Review reported Monday that McCain aides have been reaching out to key GOP activists to determine whether the Republican rank-and-file would revolt over such a pick.
The Republican operatives tell ABC that those conversations have continued into Tuesday. Top donors and convention delegates have been getting calls from high-ranking McCain associates, including Campaign Manager Rick Davis, and senior advisers Charlie Black and Carly Fiorina.
Though no names are being directly discussed, McCain is said to be considering two main candidates who describe themselves as "pro-choice": former governor Tom Ridge, R-Pa., and Sen. Joe Lieberman, I-Conn.
The calls have drawn a decidedly mixed reaction.
"They're getting a lot of pushback," one veteran Republican said, speaking on condition of anonymity. "You've got to keep the coalition together. The Republican base is just coming home."
Rush Limbaugh used his radio program Tuesday to blast the idea of McCain, R-Ariz., selecting someone who isn't a solid abortion opponent.
"If he picks a pro-choice running mate, it's not going to be pretty," Limbaugh said.