I just saw an analyst make the "don't change horses" argument with respect to national security. I think if this comes up in the course of the general election, a good answer would be along the lines of this:
Yes, it's a legitimate concern that changing administrations may open holes in our security. One good example of such a hole is the Bush administration's relaxing pressure from Al Queda when it replaced the Clinton administration. It is up to voters to decide whether this is the result of changing administrations or the result of an administration that was less focussed on national security, and to cast their votes accordingly.