Why not make it that only Veterans can run for any office?

There are a number of newly elected Veterans coming into congress. There are enough women in the forces now to represent their views. Why not simply make it a rule that only Vets can nominate, proving that you have already given your country real service seems a damned good way to improve the breed to me.
(I can't claim this as my idea. Robert Heinlein proposed "Federal Service"as a prerequisite for politics in "Starship Troopers")