Congressional Republicans are poised to release their long-anticipated tax overhaul bill Thursday, after delaying it a day to address lingering disagreements.

The GOP’s primary aim is to cut rates and simplify the tax code. The party suggested the outlines of the bill with a policy framework released on September 27, after nearly a year of hearings and internal discussions of early policy drafts.

The tax framework offered a glimpse of the tax reform debate as it unfolded. But it also excluded key details, and named certain provisions  that could change in the final bill. While there are still areas of concern and uncertainty among lawmakers and stakeholders, Congress seems to be moving in the right direction, said National Taxpayers Union executive vice president Brandon Arnold .

“I think it’s been much more a member-driven process than it was on, say, health care reform,” Arnold told InsideSources. “I think the members have had the opportunity to voice their opinions and preferences to the tax-writing committees, to leadership. It’s been a bottom-up process that I think has made the membership, generally speaking, a lot happier with their ability to weigh in.”

Republicans hope to simplify the tax system by reducing the seven current income brackets down to three, and by eliminating some deductions. They also plan to cut corporate and individual rates to lighten the tax burden many face. But, till Thursday at the earliest, the finer details of hotly awaited tax reform remain just out of reach.

“It’s also, to some of our great frustration, been a very insulated process,” Arnold said. “By that I mean there hasn’t been a lot of information that has leaked out thus far. We’ve gotten tiny bits and pieces and rumors. But for the most part leadership and the tax-writing committees have made it a very high priority to make sure that members know what the plan looks like before the lobbyists and media do. Therefore, there’s still a lot of questions that haven’t been answered yet, and won’t be answered until the official release tomorrow.”

The framework reduces the top individual tax rate from 39.6 percent down to 35 percent. It taxes middle-income earners at 25 percent, and lower-income earners at a slightly higher 12 percent. A mere outline of what may come, it did not  reveal what income levels will define each bracket. The framework also promises to boost simplicity and fairness by eliminating many itemized deductions that primarily benefit the wealthy. But it also preserves home mortgage interest, charitable contributions, work, higher education, and retirement security.

“I think one of the big question marks will be the brackets,” Arnold said. “Those have a huge impact on the distribution of taxes, particularly for lower and middle-income families. Same is true for things like the Child Tax Credit. We know it’s going to be expanded, but is that going to be $1500, $1800, $2000, or somewhere north of that. That will speak a lot to how the distribution tables are going to look.”

Republicans are also looking to spur economic growth through tax reform. In the past, they’ve considered limiting the maximum tax rate for pass-through businesses, which are often small and family-owned, to 25 percent. The framework also reduces the top corporate tax rate to 20 percent—from its current peak at 35 percent.

“The corporate tax rate, I think there’s a strong idea that is going to move to 20 percent,” Arnold said. “But is it going to be 20 percent on day one, or is there going to be a two, three, or five year phase-in process, in which case there is going to be some rumbling from the conservative and free-market crowds about getting to a competitive rate as quickly as  possible.”

President Donald Trump has expressed concern with companies outsourcing jobs to other countries. The tax bill is likely to include provisions that encourage companies to keep operations in the country: A foreign minimum tax, for one, would tax offshore profits earned by domestic companies.

“There hasn’t been a lot of color filled in on things like the foreign minimum tax,” said Arnold, who regularly testifies before Congress on fiscal policy. “There’s a lot of speculation on what that might look like, whether that will be done by countries or some kind of aggregate mechanism.”

The prospect of a border adjustment tax was raised early on as a means of keeping companies in the country. The border adjustment tax—applied when a product is produced in a foreign country but sold domestically—could also offset tax revenue lost to rate cuts. But the idea prompted infighting among party members and likely won’t be in the bill.

“The border adjustment tax is definitely off the table, but there will be something to try to prevent base erosion, trying to prevent companies from shifting their operations overseas,” Arnold said. “I think that will be the foreign minimum tax in some form or another. Hopefully, that will be a very low rate. It’s not ideal because it’s still going to add additional complexity in the tax code.”

Republicans will face pressure from various interest groups as they look to reduce tax deductions. Businesses, industry associations, and other groups benefit from the deductions and will want to defend them. Democrats, for example, were quick to denounce a plan to eliminate state and local (SALT) tax deductions. SALT deductions allow taxpayers who itemize to deduct some of their local taxes on their federal taxes.

“The lobbying campaigns have started ramping up on issues like the mortgage interest deduction, and we have the home builders and realtors grumbling about that,” as Arnold puts it. “SALT was obviously a big fight going into the budget vote, and those issues are only going to worsen going forward. There’s a delicate balance here of crafting good tax policy, and making the politics of it all work.”

The federal deficit is another looming concern with impending tax rate cuts. Most government revenue flows from taxes, a funding pool that will drain if rate cuts aren’t offset somehow. Eliminating deductions could help, but, with the full plan still in the shadows, it’s unclear to what degree.

It’s also possible taxpayers could see the addition of what would essentially amount to a fourth bracket for the lowest income earners. Republicans hope to consolidate standard deductions and personal exemptions at an increased amount. These changes would aim to create a zero percent rate by eliminating taxes on the first $24,000 of income earned by a married couple, and $12,000 earned by individuals.

“This $24,000 standard deduction, which is roughly doubling the current standard deduction, is going to take a lot of taxpayers at the lower end of the economic ladder completely off the income tax rolls,” Arnold said. “We coupled that with an expanded Child Tax Credit. You’re going to see even more people that aren’t going to have income tax liability, and people that have a middle income are going to get a big tax cut as well.”

Yet another additional bracket for the highest income earners could also be in the offing. Lawmakers might choose to add an additional top rate to ensure that the reformed tax code is at least as progressive as the current structure—so that it does not shift the tax burden from high-income to lower and middle-income taxpayers.

“The politics at the upper end of the economic ladder are a little trickier, I would say, particularly for Republicans,” Arnold noted. “But it does appear, most likely, that they are going to preserve a 39.6 percent rate, the top rate, but adjust that bracket upwards, so we’re going from about $470,000, where the bracket is now for families, all the way up to a million dollars.”

Republicans have also considered including provisions that will let businesses immediately write off the cost of new investments for at least five years. It would be a step in the right direction, Arnold said, adding that they ought to address capital investment, “moving as close to full expensing as we possibly can.”

“That is going to generate the most immediate growth and job creation out of any proposal on the table with the possible exception of corporate rate cuts,” he said. “I’m hoping that will be high on the to-do list.”

Roughly doubling standard deductions and enhancing the Child Tax Credit to leave middle-income families more money after taxes are also on the table. Republicans have also explored the idea of repealing the Alternative Minimum Tax and the estate tax—though early reports anticipate delayed estate tax repeal.

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