The Federal Trade and Communications Commissions are known buzzkills when it comes to blocking corporate mergers.

But sometimes, in the face of extreme consequences, the role falls on a higher power.

On recommendation from the Committee on Foreign Investment in the United States, the U.S. president has blocked acquisitions four times in the last three decades, each on the grounds of national security.

Such interference is a last resort, pursued only when the CFIUS deems the risks unresolvable by mitigation measures. Generally, companies abandon deals objected by CFIUS before the president gets involved.

Here are the rare instances ━ notably all involving China ━ culminating in dissolution by Executive Order: