The letter was sent to Deputy Secretary of State John Sullivan and Undersecretary of State Brian Bulatao -- not to Secretary of State Mike Pompeo. The lawmakers contend that was intentional, because they have lost faith in Pompeo’s willingness to defend the diplomats who work for him.

“His silence to date speaks volumes,” the senators wrote in the letter, led by the committee’s ranking Democrat, Sen. Bob Menendez of New Jersey.

Three U.S. diplomats are scheduled to appear in public hearings this week: William Taylor, the top U.S. official at the U.S. Embassy in Ukraine; Marie Yovanovitch, the former U.S. ambassador in Kyiv; and George Kent, a deputy assistant secretary of state in the Europe and Eurasian bureau of the State Department.

Taylor and Kent are due to testify Wednesday, while Yovanovitch is scheduled for Friday.

All three have given private testimonies to committees investigating whether Trump tried to pressure the government of Ukraine to investigate his political rivals. All three effectively defied orders from the White House and Pompeo not to cooperate with the investigation.

Their willingness to testify could affect their future job prospects, in particular for Yovanovitch and Kent, who remain in the Foreign Service.

Taylor has a five-decade long track record of government service. He was serving as a top official at the U.S. Institute of Peace before being asked a few months ago to return to Kyiv, where he’d once served as ambassador.

The senators asked Bulatao and Sullivan to respond to them in three days with an update on what steps the department is taking to support the personnel, including protecting them from any threats they may be receiving.

So far, the Democratic senators wrote, the State Department has “focused on preventing and dissuading its personnel from providing information and testimony to Congress. Many have decided, boldly, courageously, to stand up and testify nonetheless—at great personal, financial, and reputational expense.”

The State Department did not reply to a request for comment; it has largely ignored media requests related to the impeachment inquiry.

Morale at the State Department has suffered over the past two months as Pompeo has defended Trump’s actions and remained unwilling to speak out in support of diplomats caught up in the impeachment inquiry.

In a recent interview, Pompeo said he hopes “everyone who testifies will go do so truthfully, accurately.” And although he insists the State Department is cooperating with the inquiry, Democrats contend he has largely tried to stonewall.

Many members of the Civil and Foreign Service have been especially appalled at what happened to Yovanovitch: She was pulled early out of Ukraine in May after Trump’s personal attorney, Rudy Giuliani, engaged in a smear campaign against her.

Trump himself dissed Yovanovitch, who has spent more than 30 years in the Foreign Service, as “bad news” and appeared to vaguely threaten her in a July 25 call with Ukraine’s president. The content of that call is now at the center of the impeachment investigation.

