A good negotiator needs to be able to walk away.

That is a rule that, surely, Donald Trump knows. And yet in suggesting that Medicare could find big discounts by letting the government negotiate directly over drug prices, he seems to have forgotten it.

Mr. Trump has joined Hillary Clinton and Bernie Sanders in calling for a federal government program to negotiate for Medicare’s drug prices. The current system has private insurance companies each negotiating separate deals on behalf of large groups of Medicare patients. Right now, the program is O.K. at negotiating, saving as much as 30 percent off the list price of drugs, according to government reports. But Medicare still pays much, much more than government health systems in other countries.

The idea of government directly negotiating with drug makers has been a liberal favorite ever since Medicare began paying for drugs 10 years ago. You can see the appeal. The thinking goes like this: Medicare’s drug plans cover about 37 million people. Maybe if it bargained on behalf of all those beneficiaries as one, instead of dividing them into a series of smaller groups, it could get better deals. Other countries, like Britain, where the government purchases drugs for everyone in bulk, pay much, much less for drugs than the United States. In those countries, private companies don’t do the negotiating; the government does. And they don’t split the big market.

“We don’t do it,” Mr. Trump said at a Farmington, N.H., campaign event, according to The Associated Press. “Why? Because of drug companies.”