How sacrosanct is President Donald Trump’s commitment to a 20 percent corporate tax rate?

A GOP amendment to the Republican bill to overhaul the U.S. tax code that would raise the corporate rate to offset an enhanced child tax credit could put that to the test.

The measure, introduced by Sens. Marco Rubio of Florida and Mike Lee of Utah, would make the child tax credit refundable and increase the threshold for the phaseout of the credit for non-married filers to $250,000.

It would be paid for by increasing the corporate tax rate from the proposed 20 percent to 22 percent.

The current legislation would hike the tax credit from $1,000 to $2,000 per child, but Rubio and Lee have been pressing for refundability, arguing that otherwise it would not help people who really pay only payroll taxes.

While it is unlikely Rubio and Lee would gain the necessary votes from Republicans to advance it, Democrats eager to do anything they can to stop the legislation could join with a few GOP members to pass it despite opposing the underlying bill.

Rubio and Lee appeared with other GOP lawmakers and Ivanka Trump last month to expand the child tax credit.

Ivanka Trump has been traveling in India, and an aide to the White House adviser and presidential daughter did not immediately respond to a request for comment.

Along with Lee and Rubio, the amendment would also address some concerns with the current proposal from Sen. Susan Collins, R-Maine. If every Democrat supports it along with Lee, Rubio and Collins, the measure would have enough votes to pass.

Should that happen, it could set of a cascade effect that could jeopardize the entire effort.

Republicans on the Senate Finance Committee have called the reduction in the tax rate for businesses one of the cornerstones of the whole bill. And President Donald Trump has said a 20 percent corporate tax rate is the absolute highest he would support.

Whether GOP members could support a 22 percent corporate tax rate is an open question.

“A 15 percent reduction from 35 [percent] to 20 [percent] is a significant reduction, and you’re going to have some discussion here if you add anything,” Sen. Roy Blunt of Missouri said, adding that he wants to analyze the amendment before making a decision.