What the heck is Donald gonna do? Attack Hillary for feeling faint? That might make her look more sympathetic, not less qualified.
Trump has to (and should) do nothing. The video will speak for itself.
Agreed here.
This will affect Hillary in the polls. It's not a death knell; she's in the process of dying (politically) by a thousand cuts, and this is one more. It wouldn't be a problem with a candidate with a better reputation for honesty, but Hillary is a liar in the worst "lily-gilding" mode, and she now has a reputation for this.
Hillary's supporters will not leave her over this, but I suspect that this will cause SOME Republicans who are not supporting Trump right now to at least agree to vote for the Trump-Pence ticket. It's an issue that allows uncomfortable Republicans (some of them) to justify voting for a Republican candidate who is their last choice amongst Republicans. That's a loss for Hillary, and it's all because she started out with a reputation for dishonesty that grew during the campaign.