Presidential campaigns are full of promises that may or may not be kept, public personas that may or may not accurately represent the private person, partially presented policy proposals that may or may not be able to solve problems, and—new to this cycle—insults that may or may not change the way campaigns are fought in the future. In other words, it is mostly a pig in a poke that we are buying when we elect a president.

Accordingly, when presumptive Republican nominee Donald Trump says that America needs to stop subsidizing our rich allies’ security, or that he is going to build a “military much stronger than it is right now… for a lot less,” we don’t know whether he means it or not. We do know he is either showing little understanding of the complexity of governing, or he is simply not telling us like it is.

In Houston’s Republican debate, Trump was right to point out that South Koreans grow richer while American troops guard them from the strange regime to their North—something that has been going on for more than six decades. Trump wants to charge them big bucks instead. Rather than become well-paid mercenaries, as opposed to underpaid or unpaid mercenaries, it might just be better to entrust South Korea with its own defense.

But in our political system, policies are not simply a president’s choice. If elected president, Donald Trump would face the daunting task of persuading the Department of Defense,  Congress, and the public that threatening to leave will cause the South Koreans to pony up more money. Or that actually leaving is a good thing. President Jimmy Carter proposed leaving Korea more than thirty years ago, but that didn’t go anywhere.

Changes in our Korean policy would be opposed by the U.S. Army, which justifies both a role in Asia and part of its force structure with the Korean defense mission. The Army is likely to maintain that South Korea already contributes hundreds of millions each year in direct and indirect payment for U.S. forces stationed in Korea—an argument that would certainly be highlighted by the Koreans. Yet it costs billions more to recruit, train, and sustain 35,000 well-equipped troops in Korea.

South Korea will warn of dire consequences, including the acquisition of its own nuclear weapons, if we stop providing troops or charge more for them. Japan and other allies will join in lobbying efforts against significant policy changes, since U.S. forces in Korea provide a buffer for them against North Korea. China will be opposed to the nuclearization of South Korea and Japan, which it believes will jeopardize stability in the region and conjure even more concerns about North Korea. Our European allies will join the chorus, as they too benefit from U.S. security subsidies and have no interest in either paying us more or providing more of their own defense. Back at home, there will be cries that America is abandoning its global leadership role.

It would also be wonderful if we could get a more powerful military for less cost. But Trump is naïve—or insincere— when he claims that we are buying weapons only because defense industry lobbyists are pushing them, and that the military’s weapon system preferences are very different or cheaper. And the fact that this shipyard or that aircraft plant gets an extra contract is as Trump should know part of “the art of the budget deal.”

The aircraft carriers of the new Ford class are more expensive than those of the current Nimitz class not because of lobbyists or congressional campaign contributions, but because the Navy wanted the technological advances they embody. The very costly F-35 Lightning II has fans not only at Lockheed and Pratt & Whitney but also in the U.S. Marine Corps and U.S. Air Force.

President Trump will find getting others to pay for our troops stationed overseas as daunting a task as getting Americans to pay more in taxes to support our many foreign ventures. More frugal weapon deals won’t just upset contractors; the armed services Trump claims to champion would be dismayed if his proposals came to fruition.

Giving things away is better politics than paying their full costs or eliminating the spending. Trump’s campaign is built largely on the misplaced notion that he is telling uncomfortable truths. Should he find himself in the Oval Office, the Donald is the one who will face the uncomfortable truths about defense spending. Campaigning is fun, but governing is hard, even when you win.