On the first day of November, U.S. Secretary of State Mike Pompeo sent an internal email to thousands of State Department staff that began: "As champions of American diplomacy, we are in the truth-telling business."

While the email seen by Reuters focused on global policy challenges, the message extolling truth struck a nerve in a diplomatic corps immersed in an impeachment inquiry against President Donald Trump that Pompeo himself has spurned.

Next week three diplomats will be the first to testify in open hearings led by Democrats in the House of Representatives considering whether Trump should be impeached for abusing power by pressing Ukraine to investigate a rival. If so, his potential removal from office would be decided in the Senate.