Editorial: Once again, the U.S. reels from classified data leaks. This time, Ukraine’s at stake.

The gaping holes that Chelsea Manning and Edward Snowden poked into what America assumed were secure, firewalled troves of classified data taught Washington a sobering lesson about the importance of keeping secrets leakproof.

Now, however, it seems Washington needs a refresher course.

The Pentagon is scrambling to find the source responsible for a tranche of leaked documents, the release of which reveals timely information that could severely compromise Ukraine’s bid to defeat Russian forces. The task of tracking down the culprit or culprits is now in the hands of the Justice Department, which has opened an investigation.

In the short term, there’s a good deal at stake. The leaked data includes maps revealing the potential location of Ukrainian air defenses as Kyiv braces for what is expected to be a bloody, challenging escalation in fighting this spring in the country’s eastern Donbas region.

The leaked data also exposes the level of concern felt by both Kyiv and Washington over Ukraine’s dwindling stockpile of missiles to supply its air defense systems. If Ukraine is unable to replenish, the Kremlin could feel emboldened to dramatically ramp up its use of Russian fighter jets — a move that could shift the tide of the war in Russian President Vladimir Putin’s favor.

And leaked documents potentially signal to the Kremlin the methodology the U.S. is using to gather intelligence on the operations of the GRU, Russia’s military intelligence agency, and on the movements of Russia’s armed forces.

Long term, these latest leaks are likely to renew questions among America’s allies abroad about Washington’s penchant for spying on its friends.

Leaders in Seoul are certainly rankled. According to the leaked documents, the U.S. spied on South Korea and learned Seoul was worried “that the U.S. would not be the end user if South Korea were to comply with a U.S. request for ammunition.” Seoul was concerned that the U.S. would end up relaying the munitions to Ukrainian forces, which would violate South Korea’s policy of not sending armaments into a war zone. The leaked data also includes sensitive briefing content on Canada and Israel.

Spying on allies doesn’t come as any big surprise. The WikiLeaks revelations disclosed that the U.S. tapped the phone calls of then-German Chancellor Angela Merkel for years, and spied on three French presidents. But when such surveillance is disclosed to the world, it’s more than embarrassing — it sows seeds of mistrust among allies.

Barack Obama’s presidency was rocked by leaks attributed to Snowden and Manning, and Obama was right to pursue both of them criminally. Snowden, a former National Security Agency contractor, fled to Russia and in 2022 was granted citizenship by Putin. Manning served seven years in prison before Obama commuted her sentence in 2017. WikiLeaks founder Julian Assange, who published the classified information Manning, a former Army intelligence analyst, had collected, is now in a British prison as he fights extradition to the U.S.

Neither Obama nor former President Donald Trump nor President Joe Biden have been able to patch up what obviously are glaring deficiencies in the way the U.S. safeguards sensitive, classified data.

The leaks associated with Manning, Snowden and Assange may have been more embarrassing than damaging, but that’s not the case with the latest tranche of leaks. Their disclosure could work to Putin’s advantage, and it could make it doubly tough for Ukrainian President Volodymyr Zelenskyy to turn back the invasion and preserve his country’s sovereignty.

Ukrainian forces are in the midst of a critical juncture in the war. The positioning and capability of their air defense systems are vital not only to Kyiv’s push to regain more territory from Russian troops, but also to keep Putin’s MiG and Sukhoi fighter jets from entering the fray. A major step-up in the Kremlin’s use of Russian air power could seriously jeopardize Kyiv’s chances for victory.

It’s good to see that U.S. investigators are getting cooperation from Discord, an online chat service usually used by video game players, and a platform on which the leaks were posted. The documents themselves appear to be photos of classified briefing content printed out on A4 paper and folded up, as if they were shoved into a pocket before being brought out of a secure area. Strangely, some of the documents apparently had been uploaded on a Discord channel used by players of the video game Minecraft.

Finding and prosecuting the people responsible for the leaks is a must. But it’s equally important for the Biden administration to take a deep dive into shoring up cybersecurity for classified data.

Too much is at stake in Ukraine to allow this to happen again.

Snowden, Manning and Assange should have provided more than enough incentive for Washington to act decisively. It shouldn’t have to take a devastating turn of events in Ukraine for the U.S. to, once and for all, plug the leaks.

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