Late on Monday, the Washington Post published a bombshell: President Trump had shared highly sensitive, highly classified information about the ISIS fight with Russian Foreign Minister Sergei Lavrov when the two men met in the Oval Office last week.

The facts of the situation are a little murky, as the Post’s reporters (Greg Miller and Greg Jaffe) took a lot of care to avoid revealing any more classified information in their piece. But here’s what the Post scoop is clear about:

The information Trump revealed to Lavrov concerned information about an ISIS plot to bomb airplanes using laptops.

Revealing it “jeopardized a critical source of intelligence on the Islamic State,” according to the Post — specifically by giving the Russians enough information about the nature of the source to easily identify who or what it is.

That intelligence came from “espionage capabilities of a key partner,” per Jaffe and Miller. It was so sensitive that it wasn’t being shared with other allies, though we’re not sure which one it is.

Reportedly, the gaffe — something unprecedented in recent American history — came because Trump was bragging about the quality of his intelligence. “I get great intel. I have people brief me on great intel every day,” the president reportedly said.

To be clear: This isn’t illegal. The president has the power to declassify whatever he wants. So even though this information was “code-word information,” the highest level of classification there is in the US system, the very act of Trump telling it to Lavrov had the effect of declassifying it.

But this is, nonetheless, extremely dangerous. As the Post makes clear, it could have compromised a potential source of vital intelligence about ISIS plots. Depending on what the Russians do with this information, this could making the US homeland more vulnerable to attack.

More broadly, though, it raises questions about whether the Trump administration can be trusted with vital information. The US intelligence community benefits greatly from intelligence-sharing agreements with partners like the Five Eyes (FVEY) agreement with Canada, the UK, New Zealand, and Australia.

This is particularly vital when it comes to the war on ISIS. America’s partners in the Arab states — most notably Saudi Arabia, the United Arab Emirates, and Jordan — are critical sources of information on the terrorist group, some of whom have agents inside the ranks of ISIS. US intelligence services really rely on the high-quality information it gets from these states.

The fact that the president is blithely sharing sensitive information from one of these programs with the Russians may make allies think twice about continuing to share all of their vital information with the United States. That will certainly be the case for whatever ally’s intelligence methods and practices were just spilled to the Russians during Trump’s brag sessions.

Some members of Congress are already furious at the news.

“I don’t know when it will be enough for Republicans to understand that we need to get to the bottom of the connection between the president of the United States and the Russian government,” Chris Murphy, a member of the Senate Foreign Relations Committee, told reporters.

This sort of thing was a concern before Trump’s election. Some intelligence officials refused to brief Trump on vital information, the Wall Street Journal’s Shane Harris and Carol Lee reported, because they were worried he’d compromise the sources. Politico’s Nahal Toosi reported that US allies were explicitly worried that their information would get into the Kremlin’s hands, given Trump’s fondness for Putin, and were thinking about scaling back their cooperation with the US as a result.

“If there’s a sense that we’re cozying up to regimes like Vladimir Putin’s Russia, that could have something of a chilling effect," an anonymous senior Obama official told Toosi in January. "The challenge may be in places like Germany, France, potentially even the United Kingdom. If there is a reorientation toward Moscow, there could be some doubts there.”

Concerns about Trump’s ability to handle sensitive information were also fueled by photos showing the president discussing a North Korean missile test with Japanese Prime Minister Shinzo Abe at an outside table that was in full view of many other diners at the Mar-a-Lago resort.

That pales, though, when compared with what has just taken place. Whether through incompetence or an intentional attempt to curry favor with an ally, Trump has handed sensitive information over to the Russians, arguably America’s biggest adversary in the world. And the US may lose out on vital sources of intelligence about terrorism — and perhaps other subjects — as a result.

American allies with spies inside or close to ISIS already worry about the safety of their operatives and the quality of their intelligence. Now they have a new fear: that the president of the US might carelessly share it with one of the world’s most dangerous regimes.