But previous efforts failed amid opposition spurred in part by a pledge not to raise taxes from Grover Norquist’s Americans for Tax Reform that many lawmakers signed. States have been forced to supply an increasing share of transportation funding, and at least 40 states -- including many led by Republican officials -- have raised their own fuel levies since 1993, according to Moody’s Investors Service.

‘Big Believer’

In repeating his call for a reciprocal tax, Trump emphasized his enthusiasm for the approach, which resembles a system of import tariffs that would match those imposed by other countries on U.S. goods.

“I’m a big believer in a reciprocal tax,” Trump said. “If a country’s charging us 52 percent and we’re charging them nothing for the same product going back and forth? Nobody can fight it.”

Trump’s reciprocal concept differs from the “border-adjusted tax” that House Speaker Paul Ryan has proposed. Ryan’s plan calls for replacing the current corporate income tax with a 20 percent tax on U.S. companies’ domestic sales. Their imported materials would be subject to that tax, but not their exports -- hence, the “border-adjusted” description.

Trump hasn’t endorsed the border-adjustment idea, which has been vehemently opposed by retailers and other industries that rely on imports, and it wasn’t part of the outline for a tax plan that his economics aides released last week.

The nonpartisan Committee for a Responsible Federal Budget released a rough analysis saying Trump’s plan -- in its current form -- could cost $3 trillion to $7 trillion over the next decade. White House Budget Director Mick Mulvaney dismissed cost estimates of the plan on CNBC last week, saying there’s not enough detail for accurate projections.

Wants Permanent Cuts

Because the tax legislation would be unlikely to gain Democratic senators’ support, GOP leaders plan to use a procedure that would allow the measure to pass on a simple majority vote. But under that procedure, legislation can’t add to the federal deficit beyond the normal 10-year federal budgeting window.

So unless the tax plan balances any tax cuts with enough revenue-raising measures, such as ending exemptions, deductions and credits, the cuts would have to be temporary, possibly expiring within three years, based on a finding last month by the congressional Joint Committee on Taxation.