What Clandestine misses is that elections are won by who wins the moderates/independents, not based on "supporters" who are relatively evenly balanced on both sides.

Just because none of the diehard Republicans would vote for Democrats just because Swift said to does not mean that no moderates [people who go into the Presidential Debates without already having decided in their heart who the winner is] would be swayed by a Swift endorsement. Some people absolutely would.