John Bolton reportedly kept secret notes about his encounters with the president

Denis Balibouse/Reuters

• John Bolton is said to have been the most prolific note-taker at the top level of the White House. 
• Current and former senior administration officials told Axios that the former national security adviser probably has more details than any impeachment inquiry witness, so far, about President Trump's machinations on Ukraine.
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John Bolton is the impeachment inquiry's biggest wildcard. People around the president say they are worried about what notes Trump's former national security adviser has kept and when he might divulge them.

Why it matters: These sources, including both current and former senior administration officials, tell me that the former national security adviser was the most prolific note-taker at the top level of the White House and probably has more details than any impeachment inquiry witness, so far, about President Trump's machinations on Ukraine.

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