Health care reform is front-and-center on Congress' agenda, but the clock is ticking. The Senate has until Sept. 30 to pass a bill with less than 60 votes. After that deadline—whether the Graham-Cassidy bill has passed or not—it's likely the discussion will shift toward the thing many GOP leaders (including President Donald Trump) have wanted to focus on all along.

Tax reform.

It's no secret Republicans are eager to reform our tax system and consider changes to corporate tax policy. Beyond that, though, details are still a little bit sketchy and plenty complicated.

Earlier today, Veronique de Rugy, senior research fellow at the Mercatus Center, outlined three principles for tax reform. Lower the corporate tax rate (Trump favors a new rate of 15 percent, down from the current 35 percent). Pass an actual budget. And, if necessary, pay for the tax changes with spending cuts.

The final leg is the key to the whole thing, because it reveals the truth about tax reform or any other complex policy issue. It's all about Congress making actual trade-offs, rather than simply cutting taxes and adding to the federal deficit.

This is a practical rather than theoretical argument. For tax reform to pass in the Senate via the reconciliation process and without Democratic votes which it is unlikely to get, the majority must conform to the Boyd Rule, requiring that it does not add to the federal deficit.

How, then, do you make all those pieces fit together? The Tax Foundation has a few ideas. The D.C.-based think tank, which favors lower rates and a broader base for taxes, today released four potential blueprints, each with benefits and trade-offs, for Congress. Three of the four are revenue neutral. The fourth requires an estimated $70 billion in spending cuts to balance.

"The goal here to show is that there are a lot of ways to successfully achieve tax reform," said Scott Drenkard, an economist for the Tax Foundation. "This won't be easy, and everyone is going to have to give up some special provisions that currently benefit them, but the end game is lasting economic growth and higher wage."

Option A: Replace the federal corporate income tax with a 22.5 percent cash flow tax, and allow companies to expense the investments in full (as de Rugy explains, "companies generally aren't allowed to immediately deduct (expense) their investment costs when calculating taxable income and that this creates a bias against business investment"). The current seven individual tax brackets would be consolidated into three at rates of 12, 20.5, and 37 percent. The standard deduction would nearly double, from $6,350 ($12,700 married filing jointly) to $12,000 ($24,000 married filing jointly).

Projected GDP growth: 7.1 percent.

Trade-offs: It would eliminate all itemized deductions, except the home mortgage interest and the charitable contribution deductions. The home mortgage interest deduction would be capped at $500,000 of acquisition debt. Family and child benefits would be consolidated. The personal exemption would be replaced with a $500 non-refundable credit for non-child dependents.

Option B: Cut the corporate income tax rate from the current 35 percent to 15 percent. Make bonus depreciation permanent and broaden the corporate tax base by eliminating nonstructural business tax expenditures. The current seven individual tax brackets would be consolidated into three at rates of 10, 25, and 38 percent. The standard deduction would be greatly increased, from $6,350 to $50,000 for single filers (from $100,000 married filing jointly; $75,000 heads of household).

Projected GDP growth: 3.2 percent.

Trade-offs: The personal exemption and all personal credits would be eliminated, including the current Child Tax Credit and the Earned Income Tax Credit (they would be replaced by new consolidated credits: a new work credit, a new child tax credit, and a new additional child tax credit). The plan would tax all capital income (capital gains, dividends, and interest) as ordinary income. Most itemized deductions would be eliminated, but the state and local tax deduction, the home mortgage interest deduction, and the charitable contribution deduction would remain.

Option C: Cut the corporate income tax rate to 28.5 percent, and permanently extend a 50 percent bonus depreciation. Seven individual tax brackets would become four at 12.5, 25, 33, and 38 percent. The standard deduction would be increased from $6,350 ($12,700 married filing jointly; $9,350 head of household) to $7,000 ($14,000 married filing jointly; $10,500 head of household).

Projected GDP growth: 2.2 percent

Trade-offs: Distribution of taxes would remain roughly the same as today. To broaden the individual income tax base, eliminate the state and local tax deduction.

Option D: Cut the corporate net income tax rate to 25 percent, and permanently extend the 50 percent bonus depreciation. Individuals tax brackets would be consolidated the same as Option C. The standard deduction would be increased from $6,350 ($12,700 married filing jointly; $9,350 head of household) to $7,000 ($14,000 married filing jointly; $10,500 head of household).

Projected GDP growth: 3.7 percent

Trade-offs: And this is a big one. It would require $70 billion in spending cuts to meet the Boyd Rule requirements for revenue neutrality. Does Congress have the guts for that? Only time will tell.