John Bolton praised the killing of Qassem Soleimani and voiced hope it could lead to “regime change” in Iran – a longtime goal of President Trump’s former national security adviser.

Bolton, an Iran hawk, tweeted congratulations Friday to “all involved in eliminating” Soleimani and said the death of the powerful Iranian general was long in the making.

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“Hope this is the first step to regime change in Tehran,” Bolton wrote from sidelines hours after his former boss authorized the deadly airstrike at Baghdad’s international airport.

There has been some friction between Bolton and the administration since his departure. Bolton left the White House in September over foreign policy disagreements with Trump and has since forged a book deal with Simon & Schuster. He accused the White House on Nov. 22 of locking him out of his personal Twitter account potentially out of “fear of what I might say."

But White House Press Secretary Stephanie Grisham suggested the former ambassador was of “advanced age” and had simply forgotten his password.

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Bolton then credited Twitter with restoring his account and has since tweeted tough stances on North Korea and Iran and promoted his political action committee to support hawkish House and Senate candidates.

With Bolton’s support, Trump left the Obama-era Iran nuclear deal and reinstated crippling sanctions on Iran. Bolton has advocated for regime change in Iran and previously urged military strikes to take out Iran’s nuclear capabilities.

Lately, though, Bolton has been in the news for evading impeachment testimony.

Bolton is under pressure from Democrats to testify in a pending Senate impeachment trial about Trump’s efforts to withhold military aid and a White House meeting from Ukraine as he sought to secure political investigations into 2020 rival Joe Biden and his son.

His former deputy, Fiona Hill, testified Bolton was alarmed by efforts to extract an investigation out of Ukraine in return for an Oval Office visit for Ukraine’s new president.

He urged Hill to contact the White House lawyer and said he’d refuse to be part of any “drug deal” that acting White House chief of staff Mick Mulvaney and Ambassador Gordon Sondland were cooking up.

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Bolton was also frustrated with Trump lawyer Rudy Giuliani who was pushing a Ukraine policy that differed from their official positions at the National Security Council.

Bolton, according to Hill, referred to Giuliani as a “hand grenade that was going to blow everyone up.”

Senate Democratic Leader Chuck Schumer, D-N.Y., views Bolton’s information as critical to the impeachment investigation. He’s proposed Bolton; Mulvaney; Robert Blair, a Mulvaney adviser; and Michael Duffy, the point person at the Office of Management and Budget, all testify in the Senate trial.

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Senate Majority Leader Mitch McConnell, however, has not agreed to call the witnesses.

The Associated Press contributed to this report.