Donald Trump's promise to grow the U.S. economy fast enough to create 25 million new jobs over the next decade is bound to win support among American workers.

There's only one problem with his pledge.

Without a wave of new immigrants entering the American workforce, Trump will have a hard time finding enough workers to fill those jobs.

In a speech Thursday to the Economic Club of New York, Trump outlined his latest proposals to revive a U.S. economy that has shown lackluster growth in the past year. In a post on his website, he promised to raise the growth of U.S. gross domestic product to 3.5 percent a year, nearly double the average pace so far this century.

In his remarks, he suggested a 4 percent growth target was achievable.

"My great economists don't want me to say this, but I think we can do better than that," he said.

With a series of tax cuts and a moratorium on federal regulations, the GOP candidate promised that a Trump economy would also expand U.S. payrolls by 25 million new jobs over the next decade, harkening back to a period when the economy grew at a more rapid pace.

"Between World War II and the year 2000, the United States averaged a 3.5 percent growth rate," he said. "But, after China joined the World Trade Organization, our average growth rate has been reduced to only 2 percent.."

But beyond globalization, a lot has changed closer to home since those post-War boom to slow the growth of the American economy. That includes a slowdown in the growth in of the workforce.

"In the post World War II period, we had very strong labor force growth - especially with women entering the workforce in large numbers," said Chad Stone, chief economist at The Center on Budget and Policy Priorities. "Especially in the absence of immigration, those demographic trends are going to be impossible to replicate."

To be sure, millions of workers who gave up looking for a job after the Great Depression have been returning to the workforce, offsetting some of the demographic headwinds.

But an ongoing wave of aging baby boomers is leaving the labor force for good, reducing the number of workers available to fill new jobs.