A lot of people thought that Mitt Romney's Mormon faith would be an issue in the GOP primary -- it hasn't and probably won't be in this primary.
If Mitt Romney is the GOP candidate you can bet that his faith will be a hot topic in the media. But is questioning or going after Romney's faith a good thing for Obama and his team to do? I personally think that if Obama goes after Romney's faith it will backfire in a big way. Obama and his campaign will come off looking desperate and foolish for doing so.
With a struggling economy and low approval numbers, I don't think the Obama campaign will be able to resist going after Romney's faith -- they will try to scare the public of Romney's Mormon faith. With Obama's issues with the Catholic church he will come off as being a bully against religion, or anti-religion.
Politically, Romney's Mormon faith works well against a President and a media that has the perception of being anti-religion.