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Hillary Clinton’s speech attacking Donald Trump’s economic proposals on Tuesday mentioned a new analysis that says his ideas — if enacted in full — would bring about a “lengthy recession” by the end of his first term.

That report, released on Monday by Moody’s Analytics, a subsidiary of the credit rating and research agency Moody’s Corporation, explores the consequences of the policies Mr. Trump has proposed in speeches, interviews and on his website. Those policies would, under almost any scenario, result in an economy that is “more isolated and diminished,” the authors concluded.

“If Mr. Trump gets precisely what he’s proposed, then the U.S. economy will suffer meaningfully,” said Mark Zandi, chief economist at Moody’s Analytics. “It will result in a lot of lost jobs, higher unemployment, higher interest rates, lower stock prices.”

Mr. Zandi, the report’s lead author, is a registered Democrat who has donated to Mrs. Clinton. But he has worked the other side of the political aisle, too: In 2008, he advised the presidential campaign of Senator John McCain, Republican of Arizona.