This week marked the 16th anniversary of the Iraq invasion, an illegal war of aggression that was also the most purely idiotic foreign policy blunder in American history. The Vietnam debacle may have been bloodier, but at least the "domino theory" with regards to the spread of communism had a certain surface plausibility to the untutored. The Iraq invasion, by contrast, was sheerest madness — the geopolitical equivalent of someone waking up in the hospital with a crowbar through his foot after a three-week PCP bender.

As Americans look ahead to the 2020 race, it's worth asking what we can learn from this historical disaster, especially as neoconservatives attempt to gin up new wars of aggression against places like Iran or Venezuela.

The first lesson is the importance and rarity of sound, realistic judgment on foreign policy — above all in the use of military force. Washington Post columnist Max Boot is right that a big majority of the political class and population at large supported the Iraq War, but the implication is the opposite of what he claims. Far from being a difficult decision that was understandable at the time, this support betrays only that the American political class is suffused with morons and cowards. It also proves how easy it is to buffalo the population into supporting a war using lies and propaganda (especially when those lies go unchallenged by the leaders of the opposition). After all, the constant implication (known inside the administration to be false at the time) that Saddam Hussein was in league with al Qaeda was particularly effective, leading 69 percent of the population to believe he was involved in 9/11.

Still, the war was, without question, one of the easiest policy calls in American history. I was 17 years old in March 2003, and I was dead against the invasion for two reasons: 1. Notable fraud George W. Bush was pushing it; and 2. Even if the claims about nuclear weapons turned out to be true, the logic of mutually assured destruction should apply to Iraq as it did to the Soviet Union.

This reflects no special competence on my part, just the fact that any halfway skeptical teenager outside the suffocating careerism and groupthink of the Washington, D.C., foreign policy establishment could see the case for war made no sense at all.

What stands out most of all today is how the consequences of the invasion turned out to be dramatically worse than even many cynical leftists predicted. Anyone with eyes to see could tell Bush and Dick Cheney's rhetoric about nuclear weapons was duplicitous, but few predicted there would not be any WMD programs — not even chemical or biological weapons. Many thought the occupation would be violent, but not many predicted there would be eight years of apocalyptic guerrilla war, or that chaos would ignite the entire region, or that an even more murderous Islamist terrorist group would rise from the ashes. Or consider cost: In March 2003, then-Deputy Secretary of Defense Paul Wolfowitz stated that "We are talking about a country that can really finance its own reconstruction." In reality, after accounting for both direct spending and the cost of soldiers' health care, the actual cost of reconstruction will amount to over $2 trillion. Future interest payments could add even more to that number.

This bears directly on the 2020 race, as both Joe Biden and President Trump supported the invasion, while Sens. Elizabeth Warren (D-Mass.), Bernie Sanders (I-Vt.), and most other Democratic candidates did not. (Trump's assertion that he was against it from the start is a lie. He was weakly in favor beforehand and did not criticize the war effort until August 2004.) Supporting the war ought to be an absolute dealbreaker for anyone who cares about presidential judgment.

That brings me to the second major lesson the 2003 invasion can impart on us today: the value of international institutions. The United Nations Charter (which was duly passed as a treaty by the U.S. Senate) bans wars of aggression outright, stating in Article II that all members "shall settle their international disputes by peaceful means in such a manner that international peace and security, and justice, are not endangered … [they] shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state." (That is why the invasion was illegal — indeed, a war crime.)

The reasoning behind this ban on wars of aggression is straightforward — it's right there in the first sentence of the charter: "We the peoples of the United Nations determined to save succeeding generations from the scourge of war, which twice in our lifetime has brought untold sorrow to mankind[.]" More often than not, the U.S. has treated this foundational principle of the U.N. with contempt, and it simply doesn't have the power to stop us. But it's worth emphasizing this provision is aimed to prevent the devastation of war on both sides — for both aggressor and victim.

That's a lesson the U.S. could badly stand to learn as it considers the possibilities of a new president and Congress. The Iraq invasion did not destroy the U.S., of course, but it was an absolutely senseless waste of lives and resources. We are long past the point where conquering generals can bring back sacks of plunder, as in Roman times. New wars of aggression — like the ones that neoconservatives are trying to manufacture right now — will do nothing but get a lot of people killed at spectacular cost.