Former President Donald J. Trump on Monday morning claimed “inflammatory language” from Democrats had provoked what the authorities are investigating as an assassination attempt against him, urging his rivals to tone down their speech even as he called them the “enemy from within” and “the real threat.”

Hours later, Mr. Trump in a social media post sought to link both Sunday’s incident and the attempt on his life in July to statements Vice President Kamala Harris has made and to the four criminal cases he is facing.

The authorities have not yet publicly commented on a motive for the suspect, who was arrested after fleeing Mr. Trump’s golf course in West Palm Beach, Fla., on Sunday. But Mr. Trump told Fox News Digital on Monday that the gunman “believed the rhetoric of Biden and Harris, and he acted on it.”

Mr. Trump — who often uses violent language and whose frequent lies about the 2020 election led some of his supporters to violently attack the Capitol on Jan. 6, 2021 — predicted an increase in political violence in his post online, saying, “Because of this Communist Left Rhetoric, the bullets are flying, and it will only get worse!”

His statements come as he has also increasingly voiced suspicions about the attempt on his life at a rally in Butler, Pa., in July, in which one attendee was killed, two others were critically injured and Mr. Trump was struck in the ear.

Law enforcement officials have yet to identify the motives of the gunman in that shooting, who was killed by Secret Service agents. But Mr. Trump has recently pointed to President Biden and Ms. Harris: During his debate with Ms. Harris, he said that he “probably took a bullet to the head because of the things that they say about me.”

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