The GOP has used dynamic scoring to estimate the impact of its reform bill, applying assumed rates in GDP growth that are higher than assumptions from the Congressional Budget Office.

But under the Byrd rule, static scoring must be applied to budget estimates, according to a representative from CRFB.

One dramatic option for making the tax bill Byrd-compliant would be to let some portion of the corporate and individual tax cuts sunset and expire after 10 years.

Allowing the corporate rate to sunset would not be an attractive option for Republican lawmakers. CRFB notes that some conservative leaning think tanks have said doing so would undermine business investment, and potentially be more anti-growth than no cut to the corporate rate.

Making individual tax cuts temporary, as was done under the Bush administration, would also be politically perilous, as it would amount to a tax increase for households in the foreseeable future.

Some middle-class households will see tax increase

The bill being vetted by the Ways and Means Committee suffered another hit Tuesday, as the Congressional Joint Committee on Taxation released data showing some middle-class households will see their taxes go up under the TCJA.

In 2023, 20 percent of households with income between $75,000 and $100,000 will see a tax increase of more than $500; and 15 percent of households with income between $50,000 and $75,000 will see a similar increase.

About 14 percent of all taxpayers will see an increase in 2023, with wealthier taxpayers being impacted at the highest rates.

The increases are largely due to a child tax credit in the TCJA plan that is set to expire after five years. Tax writers designed the credit to sunset to accommodate deficit restrictions within the 10-year budget window.

Will they tap 401(k)s and other expenditures after all?

Democrats on the Ways and Means Committee pounced on the new data from JCT, using it to bolster their argument that individuals will suffer at the expense of lower corporate tax rates under the GOP bill.

The new JCT data may pressure the GOP to make the child tax credit permanent. But doing that would add to the bill's long-term deficit, further complicating its compliance with the Byrd rule.

As CRFB notes, tax writers in both chambers of Congress may be required to tap other large tax expenditures that were left out of the first draft bill to assure a final bill complies with the Byrd rule.

"A preferable alternative would be to make the legislation itself fiscally responsible so that it doesn't add to future deficits even when made permanent," write economists at CRFB.

That raises the question of whether the tax-preferred treatment of 401(k) contributions will reemerge as an option for making tax cuts deficit neutral.

CRFB has long advocated for an across the board cap on tax expenditures of 2 percent of income for higher wage earners.

Doing so would limit what contributions to retirement plans, employer-provided health care plans, and other popular expenditures could be written off without favoring one interest group over others.