There are some countervailing considerations to your very good point. The evangelicals who might seriously object to Romney because he is a Mormon are located in safe states anyway. Second, the Catholics are preponderant in the rust belt states running West from Pennsylvania through Iowa and to a lesser degree into Michigan, Wisconsin and Minnesota. It might be that the Catholics in these battleground states will have more of a tipping effect than southern evangelicals in safe states. For the record, I'm not asserting that Iowa predominates with Catholics.
Finally, Catholics in the Southwest might just vote that way if Rubio were the choice not just because he is Hispanic but because he is Catholic.
As the polls move more and more to Romney's favor as I expect they will, we will have much more freedom to support a running mate on ideological rather than vote gaining grounds. Yes, the vice presidency is on paper an office without any power except to break a Senate tie. Some of the most powerful men in American political history have been neutered by the office, witness Lyndon Johnson. Yet other men like Dick Cheney, have infused the office with tremendous power by virtue of their personality and the trust and confidence reposed in Cheney by President Bush. Therefore, the right man in the right relationship with Pres. Romney could exercise decisive influence for conservatism.
We must not forget that, although the office carries with it virtually no power, it is a constitutional office meaning that the Vice President is literally independent of the president, does not serve at his pleasure, and cannot be fired. So it is quite conceivable that a Vice President could turn maverick and be terribly disruptive to the smooth running of any administration. That is why Romney could never pick a Newt Gingrich as his running mate. Romney will be looking for a team player not a bombthrower. Yet, the role of the Vice President who will be selected for his team loyalty must also be the bad cop on the campaign trail to Romney's good cop. Nixon played this role to perfection. Romney will be looking for a bombthrower on the campaign trail and a team player inside the White House.
If it looks like Romney is likely to win by the time of the announcement of the running mate, I would prefer a conservative who will go rogue if he thinks his oath to the Constitution demands it rather than a political choice who will carry a critical state or two. I am not above confessing that I agree with John Kennedy said, "first you gotta win" and at no time in my lifetime has that aphorism been more relevant than today. But if we are confident of the win, I want a man who we can be sure will regard the Constitution as superior to his duty of loyalty to his boss rather than a man who will be surefooted on the campaign trail.
A conservative vice presidential nominee will balance the ticket but will he balance the presidency? That depends almost entirely on the moral character of the man.
