The baffling leak of classified U.S. intelligence documents on social media is swiftly unfurling into a debacle for the Biden administration, which is struggling to provide answers to Congress, the public and U.S. allies.

Why it matters: As President Biden kicks off his latest overseas trip — this time in Ireland, his ancestral homeland — the leak is threatening to undermine two defining planks of his foreign policy: strengthening U.S. alliances and supporting Ukraine.

• Convincing U.S. allies that "America is back" has been a central mission and challenge for Biden, who has rallied international coalitions but faced skepticism from governments that fear the return of former President Trump.
• Some experts and Western officials warn that the Pentagon leak — which reveals that the U.S. is spying on adversaries and allies alike — could erode trust and intelligence-sharing with partners at an especially sensitive moment in the global competition between the U.S. and China.

Between the lines: With so many unknowns about the origins and culprit of the leak, Republicans have largely held off on attacking the Biden administration. Some populist commentators have cited leaked details about Ukraine's military aims to bolster their case for winding down U.S. aid.

Driving the news: The documents reveal the stunning extent to which the U.S. has penetrated Russia's security and intelligence services, enabling officials to send Ukraine real-time warnings about Russian operations.

• Exposing how deeply the U.S. has compromised Russia's military apparatus could have a serious impact on Ukraine's war effort, with CNN reporting that Kyiv has already altered some battle plans because of the leak.
• The documents also suggest that the U.S. is spying on Ukraine’s top military and political leaders, as well as on other key military partners such as South Korea, Israel and Egypt.
• The South Koreans, Israelis and Ukrainians will hardly be shocked to learn the U.S. is spying on them — allies routinely collect intelligence on one another — but the disclosures are politically awkward, to say the least.

Zoom in: South Korean opposition lawmakers have reacted furiously and accused the U.S. of violating the country's sovereignty, putting President Yoon Suk Yeol in an awkward position ahead of his planned address to Congress this month.

• U.S. officials have reached out to their Israeli counterparts to reassure them after one document suggested scenarios in which Israel could be pressured to provide lethal aid to Ukraine.
• Egyptian officials today denied claims that their military was planning to secretly produce 40,000 rockets for Russia and hide it from the West — a stunning allegation against an ally that receives billions of dollars in U.S. aid.

State of play: "We don't know. We truly don't know," National Security Council spokesman John Kirby told reporters yesterday when asked if the fallout from the leak had been contained.

• The Justice Department has opened a criminal investigation, and Senate Majority Leader Chuck Schumer (D-N.Y.) has requested an all-senators briefing on leaked documents related to the war in Ukraine.
• The Pentagon’s Office of Intelligence and Security is leading an interagency probe into whether sources and methods have been compromised, a process that could take months.

What they're saying: "The Department of Defense's highest priority is the defense of our nation and our national security. The secretary and Department of Defense and the United States government take this apparent unauthorized disclosure extremely seriously, and this is a top priority for us," Pentagon spokesman Chris Meagher told reporters.