Democrat Hillary Clinton said it will be a disaster for the US economy if Republican rival Donald Trump wins the White House, warning that the "the king of debt" would cause a "Trump recession".
Mrs Clinton's speech in Columbus, Ohio, was the second in which she has argued the wealthy businessman is "temperamentally unfit" to lead the country. The first was on foreign relations and national security.
"Now I don't say this because of typical political disagreements - liberals and conservatives say Trump's ideas would be disastrous," Clinton said. "Economists on the right, the left and the centre all agree Trump would throw us back into recession."
She said Mr Trump's tax plan would benefit the rich over working families and that his promise to toss out trade deals would lead to trade wars. She also criticized his business credentials.
"Donald Trump has said he is qualified to be president because of his business record," Mrs Clinton said.
"So let's take a look at what he did for his businesses: He's written a lot of books about business. They all seem to end at Chapter 11; go figure," Mrs Clinton said, in a jab referring to Chapter 11 of the US Bankruptcy Code.
Mrs Clinton then said Mr Trump, a self-described "king of debt," had allowed businesses to amass huge debts and declare bankruptcy, leaving hundreds of people without jobs and wiping out shareholders.
Allowing the United States to accrue similar debt would rattle investors and could lead to economic catastrophe, she added.
On Twitter during Mrs Clinton's speech, Mr Trump said, "I am 'the king of debt.' That has been great for me as a businessman, but is bad for the country. I made a fortune off of debt, will fix U.S."
The tussle over the economy comes as the pair gears up for what is expected to be a fierce battle for the presidency ahead of the November election.
Mr Trump is set to deliver a speech on Wednesday in New York criticizing Mrs Clinton.
As the presumptive Democratic nominee spoke, Mr Trump's campaign tested what appeared to be a more active rapid-response operation, sending emails saying Mrs Clinton's husband, former President Bill Clinton, had backed bad trade deals and that her immigration plan would lower wages.
Mrs Clinton said Mr Trump's plan to build a wall along the US-Mexico border and deport undocumented immigrants would shake the workforce and prove disastrous for the US economy, creating a "Trump recession."