Antitrust law will probably never be the subject of breathless campaign coverage, at least not in this election year of a beauty queen and a leaked tax return. But it is one of the more powerful ways a president can shape the playing field of the United States economy.

That’s what makes Hillary Clinton’s new comments about corporate power and antitrust law important.

Her campaign has embraced an emerging line of thought in left-of-center economic circles: that a big part of what ails the United States economy are policies that have allowed the biggest companies to become too big and too powerful, resulting in less competition, less opportunity for entrepreneurship, and lower levels of investment and compensation for workers.

Notably, this is an area of economic policy in which the president has great leeway to act. If you want huge spending on public infrastructure or subsidies for college, Congress needs to agree; if you want more aggressive antitrust enforcement, you need only appoint the right people to key jobs at the Justice Department and the Federal Trade Commission.

In a speech in Toledo, Ohio, on Monday, Mrs. Clinton assailed recent bad behavior by major companies. (She mentioned Wells Fargo — which opened millions of bank accounts without customers’ permission — five times.) An accompanying fact sheet posted to her website outlined her priorities for antitrust law.