Israeli source implicated in Trump's conversation with Russians seen as key to countering ISIS threat

The classified information that President Donald Trump shared with Russian officials last week came from an Israeli source described by multiple U.S. officials as the most valuable source of information on external plotting by Islamic State.

These officials, who are privy to intelligence about the terrorist group’s efforts, said the source of information was particularly valuable for tracking Islamic State’s attempts to place explosive devices on commercial airplanes.

However, the officials disagree over how much damage Mr. Trump may have caused to counterterrorism efforts by discussing information gleaned from Israel with the Russians during an Oval Office meeting last week…

But privately, Israeli intelligence officials are fuming, one of the U.S. officials said, having worried for months that Mr. Trump would expose state secrets, even unwittingly, because of his lack of experience in handling classified information and his propensity to shoot from the hip.