Both libertarians and conservatives want to keep America safe. We differ on how best to do that. Most libertarians believe our attempts to create or support democracy around the world have made us new enemies, and done harm as well as good. We want less military spending.

Some conservatives respond to that by calling us isolationists, but we're not. I want to participate in the world; I just don't want to run it. I'm glad Americans trade with other countries -- trade both goods and people. It's great we sell foreigners our music, movies, ideas, etc. And through dealing with them, we also learn from what they do best.

On my TV show this week, former U.S. ambassador to the U.N. John Bolton will tell me why my libertarian skepticism about the importance of a "strong military presence" is "completely irrelevant to foreign policy decision-making."

Bolton thinks it's dangerous and provocative for America to appear militarily weak. He supported the Iraq War and says that if Iran were close to getting nuclear weapons, the U.S should attack. "I will go to my grave trying to prevent every new country we can find from getting nuclear weapons," because if they do, "it's going to be a very dangerous world."

He criticizes Presidents Barack Obama's and George W. Bush's failed attempts at negotiation with Iran, "negotiation based on the delusion from the get-go that Iran was ever serious about potentially giving up its nuclear weapon program."

That kind of talk makes Bolton sound like a hard-headed realist. Who wants to be naive like Bush or Obama? But hawks like Bolton ignore parts of reality, too.

They are quick and correct to point out the danger of Iran going nuclear. They are not as quick to talk about the fact that Iran has a population three times the size of Iraq's -- and the Iraq War wasn't as smooth or short as then-Vice President Dick Cheney and others assured us it would be.

If it's realistic to acknowledge that America has dangerous enemies, it's also realistic to acknowledge that going to war is not always worth the loss of money and lives, and that it makes new enemies. War, like most government plans, tends not to work out as well as planners hoped.

I asked Bolton if he thought the Vietnam War was a good intervention. "Obviously, the way it played out, it was not," he said, but, "it's always easy after the fact to second-guess."

Bolton also acknowledges that the Iraq War did not go well, but then adds, "Where mistakes were made was after the military campaign." The U.S. was unprepared for the civil war that broke out. The U.S. also failed to turn utilities and other state-run companies in Iraq over to the private sector, maintaining poorly run monopolies on energy production and other essential services, often squandering billions of dollars.

It might be seen as a harsh lesson in the importance of planning for the aftermath of toppling a bad regime. But we libertarians wonder: Why assume government will do better next time?

Occasionally government acknowledges mistakes in domestic policy -- but that doesn't mean it then becomes more efficient. It usually just spends more to try, and fail, to fix the problem. It's the nature of government. Politicians don't face the competitive incentives that force other people to make hard decisions.

Candidate Obama garnered support by criticizing Bush for costing money and lives through a protracted stay in Iraq. But that didn't stop Obama from putting more money and troops into Afghanistan.

In his first term alone, Obama spent about three times as much in Afghanistan as Bush did in two terms. Did we win hearts and minds? I don't think so. The Taliban may still retake the country.

Our military should be used for defense, not to police the world.