WASHINGTON — Promising big tax cuts and a booming economy, President Donald Trump and congressional Republicans unveiled the first major revamp of the nation's tax code in a generation Wednesday — a sweeping, nearly $6 trillion tax cut that would deeply reduce levies for corporations, simplify everyone's brackets and nearly double the standard deduction used by most Americans.

Trump said the plan would provide badly needed tax relief for the middle class. But there are too many gaps in the proposal to know how it actually would affect individual taxpayers or how much it might add to the soaring $20 trillion national debt.

There clearly would be seismic changes for businesses large and small, with implications for companies beyond U.S. borders. The American middle-class family of four could take advantage of a heftier child tax credit and other deductions but face uncertainty about the rate its household income would be taxed.

“Under our framework, we will dramatically cut the business tax rate so that American companies and American workers can beat our foreign competitors and start winning again,” Trump said.

Democrats predictably felt differently.

“Each of these proposals would result in a massive windfall for the wealthiest Americans and provide almost no relief to middle-class taxpayers who need it most,” Senate Minority Leader Chuck Schumer, D-N.Y., said at the Capitol.

Some Republicans, once fiscally demanding, shrugged off the specter of adding billions to the federal deficit.