There’s a reason why the United States never just killed Nikita Khrushchev. Or Fidel Castro. Or the ayatollah. In simplest terms: if we kill them, we make it easier for others to do the same to us.

By his title, Qassem Soleimani — the recently deceased leader of the Quds Force, the special ops component of Iran’s Islamic Revolutionary Guard Corps — may not have ranked among those heads of state. But in Iran, the Middle East, and the Muslim world, he was much more than a mere general. That’s true in the Pentagon as well. “Suleimani is arguably the most powerful and unconstrained actor in the Middle East today,” retired Gen. Stan McChrystal wrote in Foreign Policy a year ago. In August 2018, U.S. Central Command’s Gen. Joe Votel said, “Wherever you see Iranian activity, you see Qasem Soleimani, whether it is in Syria, whether it is in Iraq, whether it is in Yemen, he is there and it is the Quds force, the organization which he leads.” So killing him was not like killing, say, Votel’s successor U.S. Army Gen. Richard D. Clarke, who leads U.S. Special Operations Command, or even Russia’s military chief of staff, Gen. Valery Gerasimov. In the eyes of many, Soleimani was far more.

So now that President Trump has crossed that line, who’s next?

Why not start with Syria’s dictator Bashar al-Assad? Many have argued — Republicans and Democrats — that had President Barack Obama ordered a strike on Damascus (or at least fully armed and supported the Syrian rebels when it looked like they had a real chance) to kill Assad, whether by intention or luck of the wind, it would have prevented the prolonged civil war that has caused half a million civilian deaths, created two million refugees, and fostered ISIS and terrorist attacks in European cities. There is clear evidence that Assad is a war criminal who gassed his own women and children. He is never going to leave voluntarily. He welcomed Washington’s strategic rival Russia into his country and the region. He’s rejected all peace offerings by outside negotiators and continued to threaten U.S. personnel and interests. He has no nuclear weapons, no air force, no real military power to speak of, no friends outside of Moscow and Tehran. Just bomb him.

Related: Iran’s Soleimani Killed in Trump-Ordered Airstrike

Kim Jong-un, well, he’s a bit trickier. For starters, he has nuclear weapons. But, hey, he doesn’t have any intercontinental ballistic missiles that can reach the continental United States, or the ability to miniaturize a nuclear bomb to put on board. At least, he hasn’t publicly shown he has that capability, although the Pentagon is treating him as if he does. Kim, more than Assad, is the leader of a nation that is half personality cult, half prison. There’s likely to be support in Pyongyang for his offing, should it fall from the sky. When he came to power, the willingness of top North Korean officials to turn on each other and clean house of any adversaires with cold-blooded assassinations should be encouraging. Assassination is how they do business. The guy had his own brother killed. He killed his own uncle with a freakin’ artillery gun. The United States and the international community has made it clear it has no beef with the North Korean people; it just wants the country to stop threatening to nuke everyone else, open up its borders, and let its citizens live a free life Netflix-and-chilling among the global community for its own betterment. Killing Kim would help that along, and with the right propaganda North Koreans could be persuaded that Kim had taken them down a dangerous path. Of course, in the interim, tens of thousands of artillery shells may obliterate Seoul and U.S. bases in South Korea — but hey, as Defense Secretary Mark Esper said about Iran, enough is enough.

And just look at Xi Jinping. Smiling atop his Beijing palaces like he’s the next Mao. In the past few years, China’s leaders have taken a dark turn. Far from joining the liberal international order, the Chinese Communist Party has orchestrated a worldwide effort to infiltrate economic systems, technological structures, agricultural supplies, all while building military capability. They built islands in the ocean to expand their territory and influence, with runways to serve long-range strategic bombers — the kind that deliver nuclear weapons. The Hong Kong streets today are the living embodiment of China’s folly. Its leaders’ attempts to hold onto their iron-fisted dictatorship while living large among the global community of liberal democracies is driving the world toward conflict, not cooperation. Just ask a Uighur. China, as a matter of state policy, is undermining America’s economy, competitiveness, and ability to defend itself. It’s set its sights on Europe, Canada, and others. Enough is enough. U.S. bombers can reach Xi as fast as a drone found Soleimani. Oh, certainly, China has nuclear weapons. And ICBMs. But are they really willing to risk upsetting Donald Trump and receiving a total-wipeout retaliation of American warheads?

Finally, the most obvious next target of all: Vladimir Putin. What’s keeping Trump from dropping a bomb on Putin’s head? No, really, that’s a serious question. What do the Russians have on Trump?

Kidding. About all of this.

The killing of Qassem Soleimani is not the end of the U.S.-Iran conflict. It’s the beginning of a new era. This was no mere battlefield drone strike of a long-sought terrorist leader. Soleimani was arguably the most powerful secular leader of Iran; he operated in public internationally. Others can argue whether this technically counts as an assasination, but Trump has once again tossed a norm of political leadership out the window. The United States, in theory, does not assassinate world leaders because the international order is supposed to matter. Rule of law matters. That’s why the U.S. typically goes to Congress and international institutions like the United Nations and NATO to line up legal and political consensus and approvals before military strikes.

“Only the U.N. Security Council has the legal power to enforce international law,” said Lloyd Cutler, former White House counsel to President Jimmy Carter, laying out his case back in 1985, adding “and it in fact has no such power against the Soviet Union or the United States if either chooses to exercise its right of veto.” Cutler then points out that conservatives like columnist George Will were saying at the time that Americans shouldn’t care whether they’re following international law.

Many still feel that way, and yet the Iraq War, Afghanistan, Libya — and even Syria and strikes in far-off places like Somalia and Niger — come with some certificate of approval by others, just to be sure.

Trump, like any American president, has the right to drop a bomb anywhere at any time in the interest of national security, according to legal precedent, at least until that 60-day War Powers rule kicks in. But if Washington chooses when and where it wants to violate those rules, then, the argument goes, so can Moscow. So can Beijing. So can Pyongyang. So can Tehran. The place to solve crises with dictators is supposed to be at the United Nations and the Security Council. Or at world summits. Maybe the International Criminal Court. Or ballot boxes.

Trump is not a world leader who follows precedent. With the Soleimani assasination, Trump has ignored an unwritten rule meant to keep the world safer from political assassinations that lead to world wars. He broke a rule meant to keep him safer. In targeting his rival, Trump has made himself a target.