A boon for business?

Stock markets think a businessman president will be good for business. After dropping for a few hours following billionaire Donald Trump’s election victory, stock prices rose, and kept rising.

The markets may be right, but the Trump economy is far less certain than the early euphoria suggests.

Trump has vowed to slash taxes, dropping the federal corporate tax rate from 35 percent to 15 percent and the top individual rate from 39.6 percent to 33 percent. Lower corporate taxes would surely be a good thing—our rate is one of the highest in the developed world. Trump and the Republican Congress may team up to lower taxes, yet Senate Democrats will surely filibuster any major tax reform unless Senate Majority Leader Mitch McConnell ends filibusters, which he is clearly reluctant to do.

Wall Street also is wagging its tail at the prospect that Trump may radically revise or even repeal the 2010 financial reforms known as the Dodd-Frank Act. Here too, any changes are likely to be modest.

The Volcker Rule is a good illustration. Named for its chief cheerleader, former Federal Reserve Chairman Paul Volcker, the rule forbids ordinary banks from making investments for themselves. The rule is intended to mimic the old Glass-Steagall Act of 1933, which required that ordinary banks and investment banks be kept separate. But the ban on investing is almost impossible to enforce, and investments by ordinary banks had nothing to do with the 2008 crisis.

Repealing the Volcker Rule would remove hundreds of pages of red tape and eliminate up to $4.3 billion in compliance costs. But Trump claimed during the campaign that he would reinstate the Glass-Steagall Act—so he might not favor repeal of the Volcker Rule. Even if he did, a Democratic filibuster could stymie him. Any proposals to restructure the Consumer Financial Protection Bureau, the aggressive new consumer regulator, would meet equally fierce resistance from Democrats in Congress.

One step Trump can take on his own is to halt the Trans-Pacific Partnership trade deal, as he has repeatedly vowed to do. The trade pact would lower some of the barriers to trading between Asian countries and the United States, much as NAFTA has done with Mexico and Canada. To block the pact, Trump can simply refuse to submit it for ratification. This seems more likely to hurt the U.S. economy than to help it, however. While some U.S. businesses will benefit from protection from Asian competition, U.S. exporters and U.S. consumers will suffer.

Trump also could remove some of the restrictions Obama imposed on projects such as the Keystone XL pipeline. Bowing to pressure from environmental groups, Obama refused to approve completion of the pipeline. Reversing this policy would be a boon to the states the pipeline runs through.

A final major issue is antitrust enforcement. In the 1980s, President Reagan relaxed earlier hostility to mergers between companies in the same industry. This and his continuation of deregulation efforts in the Carter administration were among Reagan’s key economic contributions.

Trump’s antitrust policy, by contrast, is impossible to predict. He has denounced the $85 billion merger between AT&T and Time Warner, scheduled to be completed in 2017, but no one knows whether this signals aggressive antitrust enforcement or simply payback to CNN for its unflattering campaign coverage. (Time Warner owns CNN.)

When Obama was elected in 2008, his administration brought a wave of new economic regulations. Democratic nominee Hillary Clinton would have kept the regulations in place, and added more. With Trump, the future is far murkier, and the markets seem to prefer the devil they don’t know to the devils they knew.