John Bolton, the former national security adviser, reportedly became so alarmed over an effort to pressure Ukraine for political help that he told an aide to give a heads-up to White House lawyers. That's according to the New York Times, citing three people who heard the testimony of that same aide on Monday.

Fiona Hill, a former White House adviser on Russia, testified for more than 10 hours in the House impeachment inquiry which is probing President Donald Trump's pleas to Ukrainian officials for investigations into political rival Joe Biden's family and into the country's involvement in the 2016 presidential election. 

According to the Times, Hill testified that Bolton got into an argument with European Union ambassador Gordon Sondland on July 10. Sondland was reportedly working with the president's personal lawyer, Rudy Giuliani, as part of the effort to ask Ukraine for the assistance.

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Hill reportedly testified Bolton told her to inform the top lawyer for the National Security Council about the Ukraine effort that was allegedly conducted by Sondland, the president's personal lawyer Rudy Giuliani, and Acting White House Chief of Staff Mick Mulvaney. 

“I am not part of whatever drug deal Sondland and Mulvaney are cooking up,” Bolton said, reportedly according to Hill. 

Hill also said Bolton had also previously expressed concerns about Giuliani's influence.

“Giuliani’s a hand grenade who’s going to blow everybody up,” Hill reportedly said, quoting Bolton.

The interview is one of what could eventually become dozens of closed-door depositions in the impeachment probe. There are five more scheduled this week, mostly with State Department officials, though it is unclear if they will all appear after Trump declared he wouldn't cooperate with the probe.

Sondland, is expected to appear for a deposition under subpoena Thursday. He's expected to tell Congress that his text message reassuring another envoy that there was no quid pro quo in their interactions with Ukraine was based solely on what Trump told him, according to a person familiar with his coming testimony.

Also up this week: Michael McKinley, a former top aide to Secretary of State Mike Pompeo who resigned last week. McKinley, a career foreign service officer and Pompeo's de facto chief of staff, resigned Friday, ending a 37-year career. He is scheduled to testify behind closed doors Wednesday.

The committees are also scheduled to talk to Deputy Assistant Secretary of State George Kent on Tuesday and Ulrich Brechbuhl, a State Department counselor, on Thursday. On Friday, the lawmakers have scheduled an interview with Laura Cooper, who is the Deputy Assistant Secretary of Defense for Russia, Ukraine and Eurasia. It is unclear if any of those officials will show up after Trump's vow of non-cooperation.