The GOP should build on — not undo — the progress it made in 2017 with the Tax Cuts and Jobs Act.

One of the biggest wins in the Tax Cuts and Jobs Act (TCJA), the Republican tax reform law passed at the end of 2017, was the doubling of the standard deduction. That reduced the number of taxpayers for whom it was advantageous to itemize deductions. In 2017, before the TCJA, 46.8 million taxpayers itemized; the next year, only 17.5 million did so. The share of taxpayers who itemize, which was stuck around 30 percent for decades, immediately dropped post-TCJA to around 10 percent, where it has stayed in the years since.

That means about 20 percent of taxpayers who used to itemize no longer have to waste their time doing so. That’s good news for them, but it’s also good news for future tax reforms. When fewer taxpayers take advantage of carve-outs in the tax code, the carve-outs become easier to repeal entirely. Conservatives should be striving for a flatter income tax with a broader base and lower rates that is easy to pay, and the TCJA was a step in the right direction to getting there.

Aside from doubling the standard deduction, the TCJA also reduced the cap on the mortgage interest deduction from a principal of $1 million to $750,000 and capped the state and local tax (SALT) deduction at $10,000. Now, with these provisions in need of renewal by the end of 2025, some Republicans, including Donald Trump, have said they want to raise or eliminate the SALT deduction cap.

According to new analysis by Alex Brill and Kyle Pomerleau for the American Enterprise Institute, doing so would put 4–7 million taxpayers back into the itemization camp. Doubling the cap from $10,000 to $20,000 would add 4.1 million taxpayers who itemize. Raising the cap to $50,000 or more, or removing it entirely, would add 7.2 million.

The TCJA also de facto eliminated the alternative minimum tax (AMT), a complicated tax provision that creates a parallel tax system, for nearly all taxpayers. Pre-TCJA in 2017, 3.3 percent of taxpayers were subject to the AMT; after the law took effect, that dropped to 0.2 percent. Brill and Pomerleau estimate that removing the SALT deduction cap would more than triple the number of AMT filers, from 272,000 currently to 940,000.

Instead of raising or removing the cap, Republicans should be looking to eliminate the deduction entirely. With fewer people taking it, that becomes easier politically. But House Republicans in high-tax (read: Democratic-governed) states want to bring back the full deduction because some people in their districts would benefit from being able to write off their high state and local tax bills. With the House majority as small as it is, there are more than enough blue-state Republicans to cause problems for any effort to pass a tax bill.

The SALT deduction shields state-level Democrats from facing the full consequences of their fiscal irresponsibility and high taxation. Capping it has helped increase competition between states, with Republican-led states cutting their taxes and gaining population in the years since. The deduction is no doubt nice for people who live in high-tax areas, but national tax policy shouldn’t be made to appease state-level Democrats’ tax-and-spend policies. Republicans shouldn’t undo the progress they made in 2017 to make the tax code simpler and fairer for the country as a whole.