Today the U.S. underwrites the defense of wealthy nations across the globe. Washington should stop using the Pentagon as a global welfare agency.

Uncle Sam at least should charge for his defense services, as Donald Trump has suggested. America shouldn’t be defending its rich friends for free.

Most Republican Party presidential candidates insist that Washington do more on behalf of its already subsidized, protected, coddled, and reassured allies. Why do U.S. politicians put the interests of other nations before those of America?

The Pentagon devotes much of its resources to defend other nations, mostly wealthy industrialized states. In most of these cases America has no important, let alone vital, interests at stake. Instead, Washington should allow allies and friends to protect themselves.

But if Washington policymakers are determined to remain in charge irrespective of Americans’ interests, a second best would be to make those being defended pay. As Trump observed: “I keep asking, how long will we go on defending South Korea from North Korea without payment?”

How much should Washington charge? Consider some rough numbers. For instance, Washington might charge one percent of GDP for providing a standard defense.

Defending countries with globe-spanning interests could result in greater complications for America. In such cases the U.S. should add another percent to its fee.

Some nations are enmeshed in military confrontations which threaten to draw in allies and friend. Add an extra percent to the price.

An American nuclear guarantee takes the risks for America to a new level. Providing a “nuclear umbrella” warrants another one percent. Finally, countries which don’t seem interested in their own defense, or at least interested enough to spend much on their own behalf, should pay a one percent surcharge.

Such an approach would generate significant revenues for the U.S.

European states would owe a base one percent, or $185 billion. For devoting so little to the military the EU, minus the four countries spending more than two percent of GDP on the military, would have to kick in another $147 billion.

The Baltic States and Poland would owe an extra $13 billion for being involved in a potential conflicts and receiving a nuclear guarantee. France, United Kingdom, and Germany would need to kick in an extra $96 billion for extras (global interests or nuclear umbrella).

Canada would owe $18 billion. Saudi Arabia should pay three percent, or $22.4 billion: basic fee plus add-ons for potential conflict and a combination of (reduced) charges for commercial global involvement and possible nuclear guarantee. The other Gulf States should pay $8.9 billion.

Japan would owe four percent—for standard defense, nuclear umbrella, minimal military outlays, and a combination of economic international involvement and limited potential conflict—or $184 billion. South Korea would owe the standard fee plus surcharges for potential conflict and nuclear guarantee, or $42 billion. Australia should pay one percent, or $15 billion. The Philippines would owe two percent, given the potential for conflict, yielding $5.7 billion.

The grand total comes to $737 billion, which would cover the roughly $570 billion likely to be spent on the military next year. The extra would go for defense-related expenses, such as veterans’ benefits and the interest on money borrowed to pay to defend other states.

Of course, some countries might refuse to pay. But Washington should indicate that if they don’t, they will be on their own. The easiest way for states to avoid paying America for its efforts would be to defend themselves.

As I explained on Forbes online: “With the U.S. functionally bankrupt, Washington should lay down the burden of acting as the globe’s combination policeman, social engineer, and welfare agent. But if policymakers can’t get over the idea of attempting to manage the affairs of every other nation, at least they should insist on charging for services provided at American citizens’ expense. That would allow Washington to cover its own defense costs, which would be a good start.”