Secretary of State Mike Pompeo is butting heads with House Democrats beginning an impeachment inquiry against President Trump, and he’s mincing no words.

Pompeo angrily accused the Democrats of trying to “intimidate, bully and treat improperly” five current and former State Department officials.

In a letter to Rep. Eliot Engel (D-NY), chairman of the Foreign Affairs Committee, Pompeo said the proposed dates for voluntary testimony by the officials are “not feasible,” adding that “I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals.”

Pompeo’s own involvement in the investigation has broadened following a Wall Street Journal report that he was among those who listened in on the July 25 call by President Trump to Ukraine President Volodymyr Zelensky.

Prior to that report, says the Washington Post, “Pompeo had brushed off questions about the incident, saying last week that he had not yet read the transcript of the telephone call released by the White House, or the whistleblower complaint that it sparked.”

The Foreign Affairs Committee and two other House panels have subpoenaed documents and want voluntary testimony from the officials, including the former ambassador to Ukraine, Marie “Masha” Yovanovitch, and former special envoy Kurt Volker.

“Pompeo, traveling in Italy to meet with the country’s president and prime minister, ignored shouted question about the impeachment inquiry,” reports the Associated Press.

In another letter, Democratic committee chairmen anticipated Pompeo’s rejection, and added a threat.

Your failure or refusal to comply with the subpoena shall constitute evidence of obstruction of the House’s impeachment inquiry,” wrote Engel, Adam Schiff of the Intelligence Committee, and Elijah Cummings of the Oversight Committee.