John Bolton has been asked to testify in impeachment probe

President Trump’s former national security adviser John Bolton has been asked to testify before House investigators on Nov. 7, according to a copy of the request obtained by Axios. Bolton's lawyer said he would not appear voluntarily but he would accept a subpoena on Bolton's behalf, the New York Times' reports.

Why it matters: Trump's former Russia adviser Fiona Hill testified earlier this month that Bolton told a top Russia aide to notify White House lawyers about a campaign to pressure the Ukrainian government to investigate the Biden family and the 2016 election.

What they're saying: Hill said Bolton told her to alert the chief lawyer on the National Security Council that Giuliani was "cooking up" a "rogue operation" with acting White House Chief of Staff Mick Mulvaney and Gordon Sondland, the ambassador to the EU, per the Times.

• Rep. Ro Khanna, a Democrat on the Oversight committee, said that Bolton can clarify "the extent of the president's awareness" of withholding military aid and "he can talk about his own warnings to the president."
• Khanna added that Bolton could also speak to the president's awareness of arranging a meeting in exchange for a commitment from Ukrainian President Volodymyr Zelensky to open a political investigation.

Our thought bubble: ‪Bolton shares the same lawyer with former NSC official Charles Kupperman, who filed a lawsuit last week asking a federal judge to rule on whether he should testify given that Trump has asserted he is immune from the congressional process and instructed him not to appear.

The bottom line: Bolton could be a key witness in the inquiry. House Intelligence Chairman Adam Schiff said this week that he assumes the Trump administration will fight House investigators in court to keep Bolton from appearing.

Go deeper: Schiff: John Bolton is a "very important witness" in impeachment inquiry