At first glance, the kerfuffle over Donald Trump's crude remarks about women 10 years ago makes little sense: his long history of making such remarks has been discussed repeatedly over the course of the campaign, to little effect; his opponent's husband's history of sexual indiscretions and disrespect towards women is far worse, and has been so fully condoned for so long by his opponent's supporters that their criticism of Trump now reeks of hypocrisy; and he's so manifestly and direly unfit for the presidency in so many obvious ways that his boorishness really ought to be a mere afterthought by comparison. So why now, suddenly, have these decade-old salacious comments become a huge issue for the Trump campaign?
In fact, the question itself is premised on a deep, widespread misconception about the nature of political scandals. Contrary to popular belief, scandals are a symptom, not a cause, of political weakness. In the modern political environment, any politician's opponents can be relied upon to maintain a continuous stream of accusations, innuendos and condemnations related to some real or imagined misdeed or objectionable statement by their target. A politically strong public figure can parry these volleys with relative ease, refuting them or even turning them back against the accusers. If a politician weakens politically, though--if, say, his or her support appears, based on polling, to be in substantial decline--then these attacks begin to "stick", and the result is a "scandal".
Note that the substance of the scandal is irrelevant: a sufficiently strong politician can, for instance, drunkenly drive a woman off a bridge to her death and abandon her there, and survive the ordeal with only minimal political damage. A weakened politician, on the other hand, can be knocked over with a metaphorical feather: an expensive haircut, repeating one line too often at a debate, looking a bit goofy while riding a tank.
In the case of Trump, he was able to brush off lurid tales of his disgusting personal life for as long as his poll numbers remained strong. But as his popularity started to fade in early October, following a weak debate performance, he became politically vulnerable, and embarrassments he had previously been able to brush off suddenly blossomed into "scandals". It remains to be seen whether he can survive them at least until the election, but whether he does so depends on whether his declining base of support resists further deterioration--not vice versa.