Former National Security Advisor John Bolton said on Monday he would testify in the impeachment of President Donald Trump if he is subpoenaed by the Senate.  

Bolton previously refused to testify in the House of Representatives’ impeachment inquiry. In an online statement, he said, “The House has concluded its Constitutional responsibility by adopting Articles of Impeachment related to the Ukraine matter.… Since my testimony is once again at issue, I have had to resolve the serious competing issues as best I could, based on careful consideration and study. I have concluded that, if the Senate issues a subpoena for my testimony, I am prepared to testify.”

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According to a Politico source, Bolton notified Senate Majority Leader Mitch McConnell (R-Kentucky) of his decision before his announcement. A subpoena required 51 Senate votes. In a statement to Politico, Senate Minority Leader Chuck Schumer (D–New York) said, “It is now up to four Senate Republicans to support bringing in Mr. Bolton,” in reference to the four non-Democratic senators needed for the vote to pass. 

Schumer has called for White House Chief of Staff Mick Mulvaney, Mulvaney’s aide Robert Blair and senior budget official Michael Duffe to testify before the Senate. Like Bolton, all three refused to testify in the House hearings. 

If he is subpoenaed and testifies in front of the Senate, Bolton would be the most senior advisor to Trump to testify. This would give Senate Democrats the upper hand in impeachment trial. However, not many are hopeful. One Senate Republican aide told Time, “There’s a better chance he shaves his mustache.” 

Schumer, however, continues to pressure Senate Republicans, including McConnell. “If any Senate Republican opposes issuing subpoenas to the four witnesses and documents we have requested they would make absolutely clear they are participating in a cover up,” he said.