For months, Donald J. Trump and his allies have described a nation facing almost unthinkable darkness.

The United States is under “under invasion” from “thousands and thousands and thousands of terrorists,” Mr. Trump told thousands at a rally on Friday in Las Vegas. Babies are being “executed after birth.” America faces the prospect of a “nuclear holocaust.”

Three days later, after facing his second assassination attempt in two months, Mr. Trump raised what has become an all-too-common American problem: incendiary political speech. But not his — that of his rivals.

“Their rhetoric is causing me to be shot at, when I am the one who is going to save the country,” Mr. Trump said in an interview with Fox News Digital.

His remarks amount to a flip of a well-worn political script. For years, Democrats have argued that Mr. Trump’s autocratic instincts, his escalating threats to imprison those he sees as foes, his efforts to overturn the last election he lost, and his refusals to commit to accepting the results of the next one, render him a unique threat to America’s founding ideals. Dire warnings of the dangers of another Trump presidency have been accompanied by an incitement to vote, and defeat the former president at the ballot box.

Now, as part of a continued effort to deny Democrats one of their chief lines of attack against him, Mr. Trump is seeking to blame his opponents for an increasingly volatile political climate that he himself has helped stoke.

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