WASHINGTON — “Please don’t publish this letter,” Kurt D. Volker, a former career foreign service officer, pleaded in 2016 with Eliot A. Cohen and Eric Edelman, two former Republican officials leading a “Never Trump” letter-writing movement.

Their arguments were not wrong, Mr. Volker told them, as both sides remember it. But he argued that Donald J. Trump might actually win the election. And Mr. Volker, who had seen his foreign service career cut short after a new President Barack Obama swiftly removed him as the United States ambassador to NATO, was not going to blacklist himself from a senior post in another administration.

He got a lot more than he wanted.

Mr. Volker, who was President Trump’s special envoy to Ukraine until his abrupt resignation late last month, is today a central player in a political uproar that is threatening Mr. Trump’s presidency with impeachment and contaminating America’s relationship with Ukraine. It has also saddled Mr. Volker with legal bills and may force his resignation from another post, that of executive director of the McCain Institute for International Leadership at Arizona State University, based in Washington. (A final decision had been postponed.)

One bright spot for Mr. Volker, 54, a serious-looking policymaker with wire-rim glasses and a thick crop of salt-and-pepper hair, is that he was to be married Saturday afternoon at Washington National Cathedral to Ia Meurmishvili, a journalist and television anchor for Voice of America’s Georgian service. They met when he was her first guest on her television program; it is his second marriage.