The hot new policy idea in Washington is the hottest old idea: direct US military intervention in Syria’s civil war.

In the past several months, the siege of the rebel-held eastern part of the city of Aleppo has dramatized the war’s terrible cost. In the last presidential debate, Hillary Clinton proposed imposing a no-fly zone in the country and setting up “safe havens” somewhere in Syria, where neither ISIS nor Bashar al-Assad’s forces can tread. A bevy of foreign policy heavyweights, ranging from Democratic foreign policy hand Zbigniew Brzezinski to John McCain, have made similar proposals. It seems like there’s a new such proposal somewhere in the American media every day.

It’s hard not to sympathize with these calls. At least 400,000 people have been killed in Syria, and more than half of the country’s 23 million citizens have been displaced. If there’s ever a case for the use of US force, it’s stopping a catastrophe like this.

But that case assumes the policy ideas in question would actually make things better. And that’s very much in doubt for three big reasons, each of which stems from the conflict’s immense complexity. It’s hard to avoid fighting Russia, difficult to avoid sending large numbers of US ground troops, and virtually impossible to help your allies without also helping jihadists. Each of these issues, if mishandled, could end up making things in Syria worse rather than better.

I’m not saying it’s impossible to overcome the three issues. Maybe there’s a Syria plan that could. But I am saying it’s irresponsible to advocate intervening in Syria without explaining, in detail, how your plan will avoid making a terrible situation even worse.

1) How do you avoid war with Russia?

A “no-fly zone” is exactly what it sounds like: a designated area over which aircraft can’t fly without risk of interception. In Syria, this would entail US aircraft preventing Syrian government and/or Russian aircraft from flying over the designated no-fly zone, potentially by shooting down planes if necessary.

This wouldn’t solve the Syrian civil war, but it could theoretically save civilians currently being slaughtered by indiscriminate Syrian and Russian bombing runs, and strengthen the rebels by allowing them to mount operations without fear of being attacked from the sky.

But setting one up, even with the US’s dominant air capabilities, is harder than you think. First off, the US has to make sure its own planes can fly safely, which means destroying Syrian air defense and shooting down its fighters.

A detailed assessment by two US Air Force officers in War on the Rocks found that Syria’s air defense network, which includes advanced surface-to-air missile batteries, is far more robust than any other country in which the US has attempted a no-fly zone. Grounding Syria’s air force against these defenses would require a tremendous USAF commitment — one that is, in their words, “neither operationally feasible nor politically appetizing.”

And their assessment doesn’t even mention the biggest problem with a no-fly zone: Russia.

Russia is one of Assad’s most important backers, and Russian jets are currently directly striking rebel emplacements in places like Aleppo. For a no-fly zone to actually work, these Russian planes would need to be grounded. It’s not clear how to do that short of actually shooting down Russian planes.

Vladimir Putin is obsessed with sending signals of strength and weakness; it’s a key way for him to shore up his precarious political position at home. The mere fact that US planes were flying over Syria would be unlikely to cause him to back down.

In fact, it could well be the opposite: He might step up support for Assad to show the US that even the world-class USAF can’t push the Kremlin around.

“Russians might choose to escalate because they are the militarily weaker party,” Steven Cook, a senior fellow at the Council on Foreign Relations, writes. “But having gone as far as he has in Syria, can Russian President Vladimir Putin back down at the first demonstration of American power?”

In other words, the US might very well be forced to shoot down Russian jets to enforce its no-fly zone.

An air war between the US and Russia would do nothing to help the situation on the ground in Syria, while getting a lot of Americans and Russians killed. It would also raise the specter of a broader war between two nuclear-armed powers.

Outright nuclear war would, of course, remain extremely unlikely. But US-Russia fighting would make such an exchange more likely than it would be otherwise, which is pretty bad when we’re talking about something that would level every major population center in the US and Russia.

That’s a lot of risk to take on for a policy that wouldn’t even stop the Syrian civil war. People who advocate for no-fly zones, or any similar policy requiring US airstrikes on pro-Assad forces, need to explain why the risk of war with Russia is much lower than it seems.

2) How do you avoid sending in US ground troops?

A “safe haven” along the lines of what Clinton and others have suggested would involve designating an area of Syria, most likely in the country’s north, as a conflict-free zone. The idea is to create an area where civilians can settle and aid agencies can operate free of fear, alleviating humanitarian suffering and refugee outflow. Under some proposals, a safe zone would also be a haven for “moderate” rebels, a place where the US could train and equip a more effective anti-Assad fighting force.

Again, this is the kind of thing that sounds good in theory — something that wouldn’t end the civil war on its own but would help ameliorate its worst consequences. But there would be some serious consequences in practice.

The go-to example here is the Bosnian town of Srebrenica. In 1993, in the midst of the Bosnian war, the UN declared Srebrenica a safe zone for civilians displaced by the conflict, and staffed it with several hundred Dutch peacekeepers. Tens of thousands of civilians fled to the town, believing they would find true safety there.

In 1995, Bosnian Serb forces attacked the town. The peacekeepers were too weak and hampered by UN rules to stop them, and the concentration of civilians made it easier to for Serbs to kill en masse. Serbian forces murdered more than 8,000 people, in what former UN Secretary General Kofi Annan called “the worst [war crime] on European soil since the Second World War.”

The lesson for Syria is very clear: Any safe zone needs to be heavily defended, from both ground and air assaults, to prevent a replay of Srebrenica. According to one Pentagon estimate cited by Secretary of State John Kerry in February, properly securing a safe zone against a Srebrenica replay would require between 15,000 and 30,000 US ground troops.

This would, in no uncertain terms, amount to a direct US invasion of Syria. It would be the biggest US military undertaking since the Iraq War; Defense Secretary Ash Carter calls it “a difficult thing to contemplate.”

There’s very little political appetite for such a deployment, and the risks would be severe. Some are the same as a no-fly zone, such as what to do if Russia bombs the safe zone. Others, like how far into Syria US ground troops would be willing to go out of the safe zone in order to protect it, would be unique.

Once again, though, we’re talking about incredible amounts of risk for a policy that, even if it worked perfectly, would not end the Syrian civil war. Any Syria intervention plan needs to explain how it would avoid sending so many US troops into harm’s way, or explain how the policy in question would accomplish enough to justify the incredible risk created by such a large ground commitment.

3) How do you prevent jihadists from making things worse?

Many Syria intervention plans want to make the rebels strong enough either to outright defeat Assad or to threaten him enough to make him sue for peace. In order for that to happen, the rebels need more guns and more professional training. That means escalating the ongoing “train and equip” program run by the CIA, which has already funneled US support to thousands of rebel fighters.

The Obama administration just debated taking exactly this step, according to a Monday report by the Washington Post’s Greg Miller and Adam Entous. But the idea went nowhere, largely due to the myriad practical concerns with the program.

One of the main problems is that the Syrian rebels aren’t a unitary group. There’s a dizzying array of different rebel factions, and it’s hard to prevent them from sharing weapons and training. Many of the most militarily effective rebels are radical Islamists, including the al-Qaeda-linked Jabhat Fateh al-Sham (JFS).

The US tries to vet the rebel groups rigorously, but in practice distributing weapons is much harder than you might think. Just to take one example: An FBI investigation found that rogue Jordanian intelligence operatives stole millions of dollars of US weapons intended for rebels and sold them on the black market. Some of those guns were used in a shooting that killed two Americans in Amman, the Jordanian capital.

The point, then, is that the CIA program has already equipped a lot of rather unsavory people — and yet has not been able to turn the tide against Assad for good.

CIA-trained rebels are “not doing any better on the battlefield, they’re up against a more formidable adversary, and they’re increasingly dominated by extremists,” one US official told Miller and Entous. “What has this program become, and how will history record this effort?”

If that’s the status quo, then imagine stepping up the program, either by simply sending more weapons or by relaxing vetting criteria. Imagine, for example, sending the rebels advanced surface-to-air missiles to fight Assad and Russian aircraft — as they’ve requested. What happens if al-Qaeda gets its hands on them and targets commercial aircraft instead?

This is also a problem inside Syria. The more jihadists get weapons, the harder it will be for Syria to rebuild and stabilize after the war — whether Assad stays in power or is toppled. So it’s not clear that throwing tons of weapons at jihadist-linked rebels would leave Syria any better off than it would be otherwise.

This is a genuinely hard problem to solve. That’s because Syria is a genuinely hard problem to solve. The war is so complicated, with so many moving parts, that it’s hard to overstate the challenges involved in attempting to put an end to it. Any plan to fix Syria will, by necessity, be immensely complicated — and will run the risk of making an already bad situation even more deadly.

It’s incumbent on those advocating more US military intervention in Syria to take these complexities seriously — to avoid simple moralizing, casting critics as monsters indifferent to the suffering of Syrians, and address the reality on the ground with the rigor it deserves.