WASHINGTON — There is a long tradition of presidential candidates ratcheting up their language when they are trailing in the closing weeks of an election.

But in the same fashion Donald J. Trump has broken with other political traditions, he is taking a longstanding rite of fall to new heights — or perhaps new lows.

On Thursday and Friday alone, Mr. Trump unleashed a barrage of near-apocalyptic warnings about the potential destruction of the country, broad accusations about the illegitimacy of American democracy, and crude innuendo about his opponent that is almost without precedent in modern presidential history.

He warned that Hillary Clinton was conspiring with financiers to destroy American sovereignty, claimed the fate of civilization depended on his victory and ridiculed the appearance of the one of the women accusing him of sexual harassment, while also deriding Mrs. Clinton’s looks and saying she ought to be in prison. He also said the presidential election amounted to “a big ugly lie.”