Reeling from a cascade of controversial statements that drove his poll ratings down, Donald Trump sought to regain his standing Monday by laying out an economic agenda of tax cuts, vast spending on public construction and a tougher posture on trade.

“I want to jump-start America, and it won't even be that hard,” the Republican presidential nominee said in a speech to the Detroit Economic Club.

Trump's address, read from a teleprompter, was a central part of his attempt to recover from campaign turmoil that left many Americans doubting his capacity to be commander in chief.

It came as 50 senior Republican national security officials, including several members of President George W. Bush's Cabinet, signed a letter warning that Trump “would be the most reckless president in American history.”

Trump, they wrote, “lacks the character, values and experience” to be president and “would put at risk our country's national security and well-being.”

Trump said Monday their signatures make clear they're to blame for making the world so dangerous. He said they are “failed Washington elite” who must be held accountable.

Trump's claim in Detroit that his plans would spark explosive job growth left many economists skeptical, as did the absence of detail on how he would pay for his proposals.

Trump proposed tax cuts last year that would benefit primarily the wealthy and cost as much as $10 trillion over the next decade, economists say.

Trump has also promised a major buildup of the military at an unspecified price, and he has vowed to resist pressure by fellow Republicans to curb Social Security and Medicare, a pledge he did not mention Monday.

“It can't add up is the bottom line,” said Roberton Williams, a senior fellow at the Urban-Brookings Tax Policy Center, a nonpartisan think tank.

Still, the New York businessman appeared to cut the overall cost of his previous plan by making several revisions Monday.

He initially had proposed simplifying individual income tax rates with three brackets — 25 percent, 20 percent and 10 percent. Trump increased those Monday to align with a House Republican plan that calls for rates of 33 percent, 25 percent and 12 percent, and the candidate also promised that many Americans would have a tax rate of zero.

In Detroit, Trump also proposed letting parents deduct the average cost of child care spending. The plan risks favoring the higher-income taxpayers who most rely on itemized deductions, but the absence of specifics left the impact unclear.

Trump, who was interrupted by hecklers more than a dozen times, cast his Democratic rival, Hillary Clinton, as a champion of old economic ideas that have left millions of Americans unemployed or impoverished as jobs shift to foreign countries.

“Every policy she has tilts the playing field toward other countries at our expense,” Trump said.

He described the nation's economic status as far worse than official statistics would suggest, calling the 4.9 percent unemployment rate “one of the biggest hoaxes in American modern politics.”

For several days, Trump has avoided the kind of off-the-cuff remarks that have undermined his campaign. On Monday, he stuck closely to prepared remarks.

In his speech, he vowed to cut government regulations “massively,” saying President Barack Obama has imposed rules that hamstring business.

Trump also hammered Clinton for backing the North American Free Trade Agreement and a trade pact with South Korea. He predicted Clinton's campaign donors would succeed in pressuring her to renege on opposition to the proposed Trans-Pacific Partnership trade pact, which Obama supports.

On Twitter, Clinton said Trump's agenda was “a repackaging of trickle-down economics — and it doesn't help our economy or the vast majority of Americans.”

Associated Press contributed.

michael.finnegan@latimes.com