A Binder containing highly classified information related to Russian Election Interference went missing at the end of Donald Trump’s presidency, raising alarms among intelligence officials that some of the most closely guarded national security secrets from the US and its allies could be exposed, sources familiar with the matter told CNN.

Its disappearance, which has not been previously reported, was so concerning that intelligence officials briefed Senate Intelligence Committee leaders last year about the missing materials and the government’s efforts to retrieve them, the sources said.

In the two-plus years since Trump left office, the missing intelligence does not appear to have been found.

The binder contained raw intelligence the US and its NATO allies collected on Russians and Russian agents, including sources and methods that informed the US government’s assessment that Russian President Vladimir Putin sought to help Trump win the 2016 election, sources tell CNN.

The intelligence was so sensitive that lawmakers and congressional aides with top secret security clearances were able to review the material only at CIA headquarters in Langley, Virginia, where their work scrutinizing it was itself kept in a locked safe.

The binder was last seen at the White House during Trump’s final days in office. . . .

The binder was not among the classified items found in last year’s search of Trump’s Mar-a-Lago resort.