Before David Holmes came to unintentional fame as the diplomat who allegedly overheard President Trump seeking an update on politically motivated investigations in Ukraine, he was known for speaking his mind on the job.

Holmes won an award in 2014 for raising concerns about then-President Barack Obama’s policy toward Afghanistan, where Holmes had served. The “constructive dissent” honor recognizes mid-level State Department officials who use an internal process to flag problems they observe, which in his case was about how Obama had, in his view, muddied decision-making on Afghanistan and Pakistan.

A multi-layer structure installed by Obama had “hindered our diplomatic effectiveness” and made it harder for those making decisions to get a clear stream of advice, Holmes wrote in his award-winning dissent.

A write-up of the award in the Foreign Service Journal includes a photo of Holmes with Obama, whom he served as a staffer on the National Security Council.

Holmes now finds himself playing a potentially key role in House Democrats’ push to impeach Trump after his current boss, acting U.S. ambassador to Ukraine William B. Taylor Jr., revealed at a public hearing Wednesday that one of his aides overheard a phone call between U.S. Ambassador to the European Union Gordon Sondland and Trump in which they discussed the political investigations at the heart of the inquiry.

Taylor did not name the staff member, but several people familiar with the situation have confirmed that it was Holmes. He will appear on Capitol Hill on Friday afternoon for a closed-door interview with Democratic and Republican lawmakers involved in investigating whether Trump abused his office by applying improper pressure on Ukraine when he sought investigations into his Democratic political rivals.

A rising star in the Foreign Service, Holmes had a string of sought-after jobs before landing as the senior political officer at the U.S. Embassy in Kyiv.

In addition to the National Security Council — a high-stress, high-profile plum — Holmes also was picked for a prestigious job working for the State Department’s No. 3 official during the Obama administration, said people who worked with him.

“He kept getting these really significant positions because he was extremely well-regarded,” said Dan Feldman, a former State Department official who was Holmes’s superior for a time in the Afghanistan-Pakistan office.

“Those are the real brass rings of the Foreign Service. In an already disciplined, thoughtful, strategic group of people, those positions go to the ones who are particularly thoughtful and effective,” Feldman said. “He was particularly known and respected for his principled and ethical approach.”

Neither Holmes nor his lawyer, Kenneth Wainstein, responded to a request for comment.

Holmes is testifying in response to a congressional subpoena. He is surely not looking forward to it, said Ronald Neumann, president of the American Academy of Diplomacy.

“No Foreign Service officer looks with enthusiasm to being put in the middle of a political fight, a domestic political fight,” Neumann said.

“Diplomats take an oath, which is basically the same as the military takes, to the Constitution,” Neumann said. “And so when Congress under Article 1 subpoenas someone, you generally go.”

According to Taylor’s account, Holmes was at a restaurant in July when Sondland, a Trump ally, allegedly called the president on his mobile phone and told him that Ukraine was prepared to “move forward” with investigations.

That call was one day after Trump had spoken by phone with Ukrainian President Volodymyr Zelensky and asked for “a favor” in pursuing investigations of former vice president Joe Biden and his son Hunter and a debunked conspiracy theory about Ukrainian interference on behalf of 2016 Democratic candidate Hillary Clinton.

Holmes is expected to be questioned about what he overheard and about what Sondland said afterward.

Taylor told lawmakers that after the call concluded, the staffer asked Sondland, who was one of the president’s emissaries in an off-the-books effort to secure the investigations, what the president thought of Ukraine. The staffer was told that “President Trump cares more about the investigations of Biden.”

Sondland had apparently come to Kyiv to follow up on the president’s call the day before. As a political officer, it would have been customary for Holmes to accompany Sondland as he visited Ukrainian officials or to discuss those meetings with him.

“The Political Section’s top priority goals are to strengthen U.S.-Ukrainian bilateral ties and further integrate Ukraine into the Euro-Atlantic community by helping Ukraine consolidate its democracy, reinforce the rule of law, advance justice and anti-corruption reforms, bolster civil society, and promote a responsive, responsible government,” the U.S. Embassy says on its website.

Like Taylor and State Department Deputy Assistant Secretary George Kent, who both testified Wednesday, Holmes may now be cast by Trump and his allies as disloyal.

Neumann said Holmes was doing his job by reporting on what he had seen. Foreign Service officers should be protected from political retribution, he said.

Holmes faced no apparent negative fallout from his criticism in 2013, which led to the award.

“My efforts over this period, and then my formal dissent, were intended to give a voice to an important perspective that I felt lacked an advocate,” the Foreign Service Journal quotes him as saying.

William J. Burns, a retired senior ambassador, said he sought out Holmes for his staff at the State Department after being impressed with his work in India.

“David is one of those officers who gives you real hope for the future of the Foreign Service,” Burns said. “He is smart, versatile, and incredibly professional.”