Kurt Volker, the former special envoy to Ukraine, arrived at Capitol Hill to testify in private Thursday to congressional investigators who want to find out what role he may have had in President Trump’s efforts to get his Ukrainian counterpart to investigate Joe Biden and his son.

Volker resigned Friday after being asked to testify about the whistleblower’s complaint, which describes how Trump in a July 25 phone call pushed President Volodymyr Zelensky for a probe of the Bidens while the US delayed the release of military aid.

The complaint says Volker met in Kiev with Zelensky and other Ukrainian political officials a day after the call and provided advice about how to “navigate” Trump’s demands.

Volker also put Trump’s personal lawyer Rudy Giuliani in contact with a top aide to Zelensky.

Giuliani has said he was pressing Ukrainian officials to investigate Hunter Biden, the son of the former vice president and Trump’s political rival, for corruption over his dealings with a Ukrainian energy company.

Giuliani has displayed text messages with Volker that he claims prove the State Department was aware of and endorsed his push.

But current and former US officials say Volker was seeking to disentangle Giuliani’s efforts from Team Trump’s broader Ukraine policy, which is to promote counter-corruption efforts and help the country defend itself from Russian-backed separatists in its east.

On Wednesday, Secretary of State Mike Pompeo mentioned Volker’s role when he acknowledged participating in the Trump-Zekensky phone call, during which Trump sought “a favor” from the Ukrainian president.

Pompeo would not say if he thought there was anything improper about the conversation but said it took place in the context of longstanding American policy toward Ukraine.

“It’s what our team, including Ambassador Volker, what we’re focused on,” he said. “Taking down the threat that Russia poses there in Ukraine. It was about helping the Ukrainians to get graft out and corruption outside of their government.”

Separately, the Associated Press reported Wednesday that Volker met last year with a top official from the same Ukrainian energy firm that paid Hunter Biden to serve on its board. The meeting occurred even as Giuliani pressed the Ukrainian government to investigate the company and the Bidens’ involvement with it.

Democratic lawmakers said Wednesday they were prepared to subpoena White House records about Trump’s call with Zelensky.

Volker’s meeting Thursday comes after an emotional day in the impeachment inquiry Wednesday, when the president railed at journalists during a news conference with Finnish President Sauli Niinistö, used an expletive on Twitter and called the probe “a hoax and a fraud.”

The 54-year-old former US ambassador to NATO is appearing voluntarily for the interview behind closed doors with staff from the House Foreign Affairs, Intelligence and Oversight committees.

With Post wires