The last thing powerful CEOs fretting over the U.S. trade war with China need right now is to worry about higher corporate tax bills if President Donald Trump gets the boot from office in 2020.

But they may have to deal with that reality sometime in 2020 if Democratic presidential hopefuls such as Joe Biden and Bernie Sanders begin to gain traction in the polls versus Trump. Each could move to quickly reverse Trump’s signature corporate tax reform to fund various clean energy or health care initiatives, which would likely inject a new layer of uncertainty into Corporate America’s C-suites. And by extension, the stock prices of those titans of industry.

“When you look at the opportunity of what you can do, I think it would be very damaging [rolling back the president’s corporate tax cuts] because CEOs need certainty in their business. If they see rules going in one direction and then another it’s very hard to plan capital budgets and investments,” PwC U.S. Chairman Tim Ryan said on Yahoo Finance’s The First Trade.

Ryan has a unique perspective on Trump’s corporate tax reform. Not only is he a long-time accountant, but his position atop consulting giant PwC lands him in more than 400 meetings annually with the country’s top CEOs.

“So I think any type of shock to the system where we had a big benefit to the system from tax reform and then it’s taken away and that ultimately de-stimulates [the economy],” Ryan explained.

Whether Trump’s corporate tax cuts in 2017 have truly helped the middle class (or anyone) will be debated for decades. But one thing that can’t be argued is that the cuts to 21% from 35% sent companies on a stock buyback binge.

Stock buybacks surged more than 60% in 2018. The $1.1 trillion-plus in announced buybacks last year marked a record.

Meanwhile, capital investment rose by about 6% in 2018 — somewhat of a letdown, but up nonetheless.

“Without a doubt the tax plan has helped. We see it in stock prices, employees — the U.S. is still the best game in town. Companies still want to come here,” added Ryan.

Brian Sozzi is an editor-at-large and co-host of The First Trade at Yahoo Finance. Follow Brian Sozzi him on Twitter @BrianSozzi

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