The Latest: Trump says lower corporate rate 'non-negotiable'

The Latest on President Donald Trump's tax cut proposal (all times local):

8:05 a.m.

President Donald Trump says reducing the corporate tax rate to 20 percent is a "non-negotiable" part of his tax plan.

Trump tells "Fox & Friends" that he wanted to go lower, but "the numbers really work at 20."

The president and congressional Republicans came out with their tax overhaul plan on Wednesday. Under the plan, corporations would see their top tax rate cut from 35 percent to 20 percent.

Trump says the overall plan would provide tax relief for the middle class.

But there are too many unknowns in the proposal right now to know how it actually would affect taxpayers.

In his latest tweet, Trump notes Democratic opposition to the plan. He says: "Democrats don't want massive tax cuts - how does that win elections? Great reviews for Tax Cut and Reform Bill."

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7:15 a.m.

President Donald Trump's White House economic adviser is asserting that the administration's proposed tax cut is "purely aimed at middle class families."

Gary Cohn says in a nationally broadcast interview that a hypothetical family of four should have "a substantial tax decrease."

Pressed on this point in an appearance Thursday on ABC's "Good Morning America," Cohn estimated the tax relief for such a family should be in the range of $650 to $1,000. "We've doubled the amount of income that people can keep in the zero tax rate," Cohn said.

He also argued that "the wealthy are not getting a tax cut under our plan." Cohn demurred on questions about how much Trump would benefit by the proposed change to the U.S. Tax Code, but said "we are very confident that Americans are getting a great deal."

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3:50 a.m.

How do you pay for an estimated $5.8 trillion tax cut?

For President Donald Trump and Republican congressional leaders, that is the mostly unanswered $5,800,000,000,000 question.

The plan they released Wednesday took a first step toward outlining how Republicans propose to cover some of the monumental cost over the next 10 years, mainly by removing certain tax breaks. But even those proposed changes were left vague — and wouldn't remotely pay the full cost of the tax cut.

The administration says it would eliminate most personal tax breaks. Possibly gone would be people's ability to deduct state and local taxes as well as eligible medical expenses. But doing so would still leave the tax cut more than $2 trillion shy of paying for itself.