McCain's stance also appeals to centrist evangelicals, who have been attracted to him by his opposition to abortion combined with his call for action on climate change and his resolute condemnation of the use of torture by US forces.
But his trump card with evangelicals could be a joker if he plays it badly in his bid to woo centrists and independents.
"For the Republicans it is a wedge issue because their right wing is very vocal on it. To bring it up at all you either risk the wrath of the right or you risk sounding too extremist to the middle," said David Epstein, a political scientist at Columbia University.
OBAMA'S HAND?
Is this an advantage for Obama?
"The Democrats can take a pro-choice position and...appeal to their base and to the middle," said Epstein.
Allen Hertzke, director of Religious Studies at the University of Oklahoma in Norman, said it could help Obama secure support from some of the white women who voted in droves in the Democratic nominating contests for Senator Hillary Clinton, who is running behind Obama for the party's presidential nomination.
But the issue is not a clear-cut one along gender lines.
"Some of the white working class women especially Catholics who supported Clinton are also pro-life and if abortion becomes salient it could hurt Obama among this group," he said.
Hot-button issues like abortion and gay marriage were important in 2004 when President George W Bush got close to 80 per cent of the votes cast by white evangelical Protestants.
However, white Catholic women who oppose abortion but voted for Clinton may well be focused on the dire state of the US economy, which Hertzke said was a clear plus for Obama.
Analysts said both sides could also pitch the issue to their bases as a struggle over the composition of the US Supreme Court whose justices are appointed by the president.
The anti-abortion rights movement has long had its eye on the big prize - a decisive conservative majority which would overturn the 1973 Roe v Wade decision granting women the right to an abortion.
McCain has reiterated that he would appoint such justices; for the Democratic base it is seen as vital that the tide of conservative appointees on the bench be rolled back.
Opinion polls consistently show that the parties' starkly different opinions on the issue are not held by large swathes of the middle in America. They show most Americans broadly support abortion rights but are less comfortable with the procedure in the later stages of pregnancy.
