US President Donald Trump speaks about the passage of tax reform legislation on the South Lawn of the White House in Washington, DC, December 20, 2017.

"Not only will this tax plan pay for itself, but it will pay down debt," Treasury Secretary Steven Mnuchin asserted as Congress debated the Trump tax cut. Mnuchin named two factors — increased economic growth and reduced corporate tax avoidance — that would offset revenue losses from lower rates.

That claim was politically important for congressional Republicans. They relentlessly attacked President Barack Obama for increasing deficits and debt.

His own advisors knew that was impossible, so Trump sharply pared back this proposal. But he continued to maintain the deficit wouldn't rise.

Those claims date back to Trump's 2016 presidential campaign. He first proposed a $10 trillion tax cut far larger than any Republican rival's, but insisted it wouldn't boost the federal budget deficit even temporarily because the economy would "take off like a rocket ship."

Presidents often make extravagant claims for their policies. But rarely are they proven so false so fast as Donald Trump 's claims about tax cuts and deficits.

"The years when we increased deficits are years when the economy is slowing down," said Gary Cohn, then director of the National Economic Council. He explained lower rates would lead corporations to shift taxable operations back to the U.S. from abroad.

House and Senate leaders used those arguments to reassure Republican holdouts. "We're right there in the sweet spot with economic growth that gives us more revenue," Speaker Paul Ryan declared.

"We fully anticipate," said Senate Majority Leader Mitch McConnell, "this tax proposal in the end to be revenue neutral for the government if not a revenue generator."

A few skeptics worried anyway. Calling debt "the greatest threat to our nation," Sen. Bob Corker of Tennessee vowed to oppose it "if it looks like to me … that we are adding one penny to the deficit."

He had good reason for skepticism. Deficits rose after tax cuts under Republican Presidents Ronald Reagan and George W. Bush. Independent economic forecasters, liberal and conservative alike, projected the pattern would repeat.

Ultimately Corker joined fellow Republicans in finding reasons to go along. Having failed to repeal Obamacare, they yearned for a legislative victory.

Some considered tax cuts their highest priority. Others privately welcomed deficits as a prod to shrinking government. Still others resolved their ambivalence by siding with their party.

"There are about as many economists as there are opinions," said Rep. Tom Cole of Oklahoma. "In the end I'm going to trust the people who are philosophically aligned with me."

In June, six months after the tax cut passed, Cohn's successor, Larry Kudlow, claimed the deficit "is coming down rapidly" due to economic growth. Now, the government Trump oversees has demonstrated the opposite.

Even as growth has accelerated, the Treasury reported that the 2018 deficit swelled to $779 billion. That level, the highest in six years, marks a 17 percent increase over 2017.

Federal spending as a share of the economy fell. But revenue fell even more, with corporate tax receipts plummeting 31 percent. The Congressional Budget Office forecasts deficits hitting $981 billion in 2019 and exceeding $1 trillion every year after that.