But it also presents a global security risk. A building branded with the name of an American president — any president, but perhaps especially Mr. Trump — would be a tempting target for terrorists and other enemies of the United States. Who is going to protect the buildings? Will the Trump organization hire a security firm to do the job, or will the American taxpayer be on the line for the bill? Will foreign governments offer to pay to secure the properties — a subsidy of the Trump organization that would probably violate the Emoluments Clause? If a terrorist attack, a botched security operation or some other tragedy happens on a Trump property, the United States could easily get drawn into a conflict abroad. And our adversaries know this. This is one of the most dangerous aspects of Mr. Trump’s conflict-of-interest problem.

Then there is the litigation risk. In Clinton v. Jones, the Supreme Court ruled that the president can be sued in his personal capacity and required to testify in depositions and at trial. Sexual misconduct is a litigation magnet; extensive business operations are another. If Mr. Trump owns his businesses while he is president, it will be a lot easier for plaintiffs’ lawyers to sue him on behalf of customers, counterparties, investors and others, and to require his testimony under oath.

The Trump University case settled for $25 million shortly after the election, and lawyers will be looking for other quick and profitable settlements from a president who does not want to be embarrassed by litigation. As plaintiffs’ lawyers pile on, they will be egged on, and perhaps subsidized by, the president’s political opponents, as happened in the Paula Jones case against Bill Clinton. How can Mr. Trump focus on defending the country if he has to waste time defending himself in court?

The fundamental problem, of course, is one the founders envisioned: They did not want our government officials being paid off by foreign sovereigns. This is why the Constitution has the Emoluments Clause. We also have criminal statutes barring any quid pro quo involving public officials (bribery, solicitation of a bribe or offering of a bribe).