Republicans love tax cuts, and both President Trump and Speaker Ryan have set their sights on lowering both personal and corporate income tax rates. But some Republicans also like controlling the budget deficit, while others favor defense spending or immigration control. How can the GOP cut tax rates, raise defense spending and immigration enforcement, and control the budget deficit? Here’s the heart of the problem: the federal government gets roughly $1.4T from income taxes, $440B from corporate income taxes and capital gains, $1.1T from payroll taxes, and smaller amounts from other sources [1]. The tax plan under consideration will substantially cut the first two sources, without raising the other categories. How can such a tax plan be implemented without blowing up the budget deficit?

The evolving Trump-Ryan plan bridges this gap by introducing a new category: a border adjustment tax on imports. If all 2.7T in US imports were taxed at 20%, this could raise over $500B per year, providing a source for big tax cuts (though still not enough to pay for the tax cuts proposed). But there’s a problem with this idea – will 50 Republican senators vote for it?

The National Retail Federation has come out strongly against the plan, as have the Koch brothers, whose companies participate heavily in international trade. The Kochs are focusing their battle charge in 15 states where they may be able to sway Senate votes. Meanwhile, with retail giant WalMart strongly opposed, will the senators from Wal-Mart… err Arkansas be on board?

Hence we have a GOP civil war, pitting major exporters like Boeing, Oracle, and GE against retailers and other importers, and pitting nationalist Republicans versus traditional free-trade Republicans.

Trump and Ryan can only spare two votes in the Senate – will they be able to keep everyone on board? While the plan could stimulate US growth through tax cuts and favoring US production, it may also trigger a trade war that nullifies much of its benefit. There’s also the essential nature of the import tax – it is effectively introducing a new US consumption tax for the first time. Consumption taxes have been on the GOP radar for some time, as they tend to shift tax burdens down the income scale, and to reduce taxes on the wealthy. But is Trump’s base ready to pay an extra 40 cents at the pump every day, when many of them won’t see a huge tax cut [2]? Let the Republican tax civil war begin.

[1] The CBO provides a detailed breakdown of revenues here. I have combined corporate taxes and capital gains into one category, as both are taxes on capital.

[2] Roughly 50% of oil is still imported into the US, so a border adjustment tax could disproportionately increase oil prices.