The original proposal had also represented an attempt to align tax rates for small and large businesses. Trump has proposed a 15 percent rate for C corporations -- down from the current top statutory rate of 35 percent. Now, according to the foundation’s analysis, the plan is unclear.

“As of today, the campaign is unclear as to whether it will apply its 15 percent corporate rate just to traditional C corporations, or to both C corporations and pass-through businesses,” the Tax Foundation said in a statement that accompanied its new analysis Monday morning.

Bloomberg News and other news outlets reported last week that Trump had dropped his proposal to create a new 15 percent tax rate on business income from partnerships and other pass-throughs from the latest version of his plan.

Cole, of the Tax Foundation, said Trump’s campaign told him via e-mail on Thursday that, going forward, “the 15 percent rate only applies to businesses that are taxed as corporations.”

Initial Estimate

That day, Cole released an initial cost analysis for Trump’s latest plan of $4.4 trillion, before considering the effects of economic growth. That number, which Trump also cited in a Thursday speech to the Economic Club of New York, was based on calculations that didn’t include the special pass-through tax rate.

But the New York Times reported Friday that Trump’s campaign had assured the National Federation of Independent Business, which represents small businesses, that Trump remained committed to the proposal. Confusion reigned through the weekend as Trump’s advisers said in statements to various media outlets that small businesses could indeed use the 15 percent rate.

“This rate is available to all businesses, both big and small, that want to retain the profits within the business,” said a note on the website.

But if businesses retain profit, they are no longer operating as pass-throughs; instead they’d resemble regular corporations. In his latest analysis Monday, Cole of the Tax Foundation acknowledged the lack of clarity and sought to sort it out.

Two Estimates