The official, Lt. Col. Alexander Vindman, told impeachment investigators that he tried unsuccessfully to have the omissions restored. They included mentions of Joe Biden and Burisma, the energy company whose board employed Mr. Biden’s son Hunter.

Colonel Vindman didn’t testify to a motive behind the White House editing process, but the omissions don’t fundamentally change lawmakers’ understanding of the call.

Reaction: Right-wing commentators have questioned the patriotism of Colonel Vindman, a Ukrainian-American immigrant who received a Purple Heart after he was wounded in Iraq.

Another angle: Robert Livingston, a former Republican congressman turned lobbyist, repeatedly told a White House official that the U.S. ambassador to Ukraine should be fired because of her association with Democrats, the official plans to tell investigators today.

Related: House Democrats released their proposed rules for impeachment proceedings. The plan, which is scheduled to come up for a vote on Thursday, would require the production of a public report and allow for due process rights for President Trump.