Vice-presidential candidates customarily do not drive vote choices, but there may be an exception: 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 in this ABC News/Washington Post poll say they'd be less likely to vote for him if he picked a candidate for vice president who favors legal abortion, vs. 10 percent more likely – a 10-point net negative, and one he does not make up among Barack Obama's supporters.
The potential damage is sharper in some groups. Twenty-seven percent of conservatives say they'd be less likely to support McCain if he picked a vice president who favors legal abortion, vs. just 3 percent more likely – a net 24-point negative in this heavily Republican group. It's similar among evangelical white Protestants; 29 percent say such a pick would make them less likely to vote for McCain, vs. 6 percent more likely, a 23-point net negative.
The effect is biggest, naturally, among the 41 percent of registered voters who oppose legal abortion in all or most cases. A 32-point net in this group say a running mate who supports legal abortion would make them less likely to vote for McCain. And it would be a 42-point net negative to the most strongly anti-abortion voters, those who say it should be illegal in all cases. Anti-abortion voters, like evangelicals and conservatives, are among McCain's strongest support groups.
It's not only in the base that McCain could be hurt by a running mate who favors legal abortion. While there's no apparent effect among all movable voters (those who say they might change their minds or have no preference), among independents who are movable the proposition gets a 16-point net negative response.
While he could lose votes in these groups, moreover, McCain looks less likely to gain much support among their opposites. It would be just a 6-point net positive for him among all voters who support legal abortion, rising to 18 points among those who support it most broadly (in all cases). It looks apt to help him even less among liberals, moderates and non-evangelicals.
The net among all registered voters is that 9 percent say they'd be more apt to support McCain with a running mate who favors legal abortion, but 19 percent said it would make them less likely to vote for the Republican ticket.
These compare to the anticipated impact of Joe Biden on the Democratic ticket. In interviews before that pick was announced, 13 percent said it would make them more likely to support Barack Obama, 10 percent less likely – essentially no effect, given polling tolerances. Seventy-five percent said it would make no difference.
McCain floated the possibility of a running mate who supports legal abortion two weeks ago, saying that this would not necessarily rule out Tom Ridge, the former Pennsylvania governor. Said McCain: "I think it's a fundamental tenet of our party to be pro-life but that does not mean we exclude people from our party that are pro-choice."