She was not being adversarial. She was actually trying to help him. She gave him every opportunity to take a firm stand and he just kept going wobbly. She was lobbing him softballs and he was swinging and missing. She sounded adversarial because she couldn't get him to connect with her softball pitches.
Kerry can't be helped.
Diane's mistake was in asking him a direct question to which Kerry cannot answer either way. If it's "worth it," then Kerry's whole line of attack against Bush is kaput. If it's "not worth it," then Kerry sets himself for an incredible thrashing on a variety of fronts.
If he were a man of principle (he's neither), then Kerry could simply say "no, it's not worth it." He'd be wrong, but at least he would be honest, and he'd probably be 10 points up on Bush right now.
Bush, meanwhile, unbothered by the need to answer with "what will sound most popular," gets to be consistent.