WASHINGTON (AP) — Does money roll downhill?

In their drive to cut taxes, President Donald Trump and congressional Republicans are betting it does.

Behind their legislation is a theory long popular among conservatives: Slash taxes for corporations and rich people, who will then hire, invest and profit — and cause money to trickle into the pockets of ordinary Americans. The White House says the plan's corporate tax cut alone would eventually raise average household incomes by $4,000 a year.

The tax plan's "trickle-down" approach was popularized in the 1980s during the Reagan administration, thou...