Matthew Dowd claims not:
Today, the myth is repeated over and over that Bush beat Kerry in Ohio in part because of the gay marriage initiative on the ballot. The facts and data simply do not support that conclusion. Yes, conservative turnout was up in Ohio by five percentage points. It was also up five percentage points nationally. And if you look at the conservative turnout increase in the 11 states verses the other 39 states that didn’t have gay marriage on the ballot, the conservative turnout was up exactly the same. Further, if you look at white evangelical and conservative turnout in swing states with gay marriage initiatives versus swing states without them (like Florida, Pennsylvania and Nevada), again, there is no statistical difference in turnout increases among these groups. Yes, that is right, increase in turnout among key conservative groups did not vary between swing states with and without these initiatives on the ballot.
The Dish 