With Republicans occupying the White House and comprising majorities in Congress, CFOs have good reason to be optimistic about their employers’ tax prospects. After all, there is widespread agreement that the current 35% corporate income tax rate should be slashed to at least 20% (the House of Representatives Plan) or even as low as 15% (President Trump’s proposal during his candidacy).

Beyond tax cuts, however, the tax reform outlook begins to blur.

A centerpiece of the reform blueprint that House members are counting on to pay for the revenue lost via lower tax rates, the so-called “border-adjusted tax,” has been vigorously opposed by the retail and energy industries and other groups heavily reliant on imports. It’s also gained a lukewarm reception from President Trump, who has seemed to favor a simpler, more protectionist tax system. To be sure, the balance could shift toward such a tax if the president signals a change of heart toward border adjustment in his address to a joint session of Congress on Tuesday.

Still, writes Nate Smith in this special report on Smart Tax Planning, the tax might hit a wall when it comes to approval by the World Trade Organization. That’s because the WTO forbids direct taxation on corporate incomes stemming from exports and imports, which the House Plan would retain to some degree. “Although many support the proposed border-adjustment provisions in the plan, radical changes are likely to be necessary to realize the plan’s vision,” Smith writes.

The uncertainties extend beyond the fate of border-adjustment taxes to whether a territorial tax system can be set up in the United States, what repeal of the Affordable Care Act (if it happens) will mean for corporate taxes, what federal reforms will mean on the state level, and more. Yet while planning with all these wild cards on the table will be hard in the coming months, the authors of this report say, CFOs can sketch out scenarios that will enable them to proceed in realizing their companies’ goals.