But this was the first time that Mr. Trump has directly accused China of interfering in American politics in an effort to challenge him. And it is at odds with his repeated comments that he has a strong relationship with China’s leader, Xi Jinping, who presumably has had a strong hand in each of the retaliatory actions taken by Beijing.

A month ago, the director of national intelligence, Dan Coates, warned that the “system is blinking red” for the coming elections. But he was referring chiefly to fears of Russian activity, his aides said at the time, and he made almost no mention of China. —DAVID E. SANGER

Trump turns down meeting with Trudeau

During a news conference, President Trump confirmed that he rejected a one-on-one meeting with Prime Minister Justin Trudeau and slammed Canada for recent disagreements over trade.

“Frankly, we are thinking about just taxing cars that are coming in from Canada,” Mr. Trump said. “We are very unhappy with the negotiations — with the negotiating style — of Canada.”

He went on to criticize Canada’s negotiations over the Nafta trade deal — an agreement he called “very bad for the U.S.” — and the recent tariffs put in place on American-made products.

“Canada has treated us very badly, they have treated our farmers in Wisconsin and New York State very badly,” he said. “So Canada has a long way to go, I must be honest with you, we are not getting along with their negotiators at all.”

While he did not rule out the prospect of a new trade deal with Canada, he said it would probably be very different from what the Canadians are seeking. — MEGAN SPECIA