-- It is far easier to argue that your opponent is not fit to serve if you can provide confidence that you are fit to serve yourself.
In a measure of how difficult this may be for Clinton to muddle through, Trump and his campaign have shown uncharacteristic initial restraint. They realize that this is a mess of Clinton's creation and that how she deals with it could have far-reaching ramifications for the balance of the race.
Within moments of the episode, the Clinton campaign went into a vaguely familiar lockdown mode. When word did emerge from the campaign, the official account was that Clinton felt overheated at a 9/11 remembrance event and was feeling "much better" — a story that seemed incomplete in light of video evidence that quickly surfaced.
All this may have been hard enough to believe on its face had Clinton and her aides not had a history of misleading the press and public when it comes to her health. The full story of her fainting spell in 2012, when she was secretary of state, may still not be known, and it began to be told only when glasses she wore in public testimony revealed a more complicated truth.
Earlier this year, in relation to the unrelated matter of her personal email, Clinton declared that she was the "most transparent official in modern times." That statement strains basic credulity — now more than ever.
Clinton allies will argue that she has provided more health-related details, not to mention vastly more financial and professional information, than Trump. That is inarguable.
It is also, for now, beside the point. After just this one ill-timed health scare and in the course of just a few hours, Clinton's campaign reinforced concerns about her honesty and accountability. The timing also happened to play into a Trump campaign line of attack about her stamina and overall health.
Just last week, when asked about her health, Clinton declared, "I'm not concerned about the conspiracy theories."
But when events and actions reinforce those storylines, it's time to be concerned. Those theories will harden and go mainstream, until or unless the campaign addresses them not with accusations and partial accounts but with solid information.