But see also Aaron Blake at The Fix, "Obama’s gay marriage position could be problematic, poll shows":
Six in 10 Americans say President Obama’s embrace of gay marriage will have no impact on their vote this year, according to a new Gallup poll. But of the rest, twice as many say it makes them less likely to support the president.More at Memeorandum.
Twenty-six percent of Americans in the poll said Obama’s switch on the issue makes them less likely to vote for him this November, compared to 13 percent who said it makes them more likely to support him....
We have long known that the enthusiasm on this issue resides largely on the anti-gay marriage side, and this poll reflects that. Even though a majority of Americans — 51 percent — say they approve of Obama’s decision (compared to 45 percent who disapprove), the fact is that supporters are significantly less avid than opponents.
While a strong majority of Americans says this issue has no impact on their votes, the fact that it matters to nearly 40 percent of Americans isn’t insignificant.
And if Obama forfeits some Democratic and independent votes in a tight race, that could matter.