Former Sen. Joe Lieberman has gone from front runner to out of the running in President Trump's effort to fill the vacant FBI director's job, a senior White House official told Fox News on Wednesday.

Before Trump left for an extended overseas tour last Friday, he told reporters the ex-Connecticut lawmaker, a Democrat-turned-Independent, was the leading candidate to replace James Comey, who was fired by Trump on May 9.

But things have changed, in part due to Trump's hiring of an attorney who works at the same firm as Lieberman. Marc Kasowitz, who has worked for Trump in the past, was brought on to represent the president in the ongoing Russian election meddling probe. Lieberman is a partner of Kasowitz’s New York law firm, Kasowitz, Benson, Torres.

With the FBI involved in the investigation, sources said installing Lieberman to head the bureau could present a potential conflict of interest.

Kasowitz is not the first attorney from the law firm to serve Trump or his administration. The firm, just last year, was known as Kasowitz, Benson, Torres and Friedman, but Friedman—David Friedman—is now Ambassador to Israel.

It was just last week when Trump told reporters in the Oval Office that he was “very close” to naming a new FBI director, and when asked point-blank if Lieberman was the leading contender, Trump replied, “Yes.”

Lieberman, 75, has extensive law enforcement experience. He was a two-term attorney general for the state of Connecticut, spanning from 1983 until his resignation in 1989 when he was elected to the U.S. Senate, serving from 1989 until 2013- first as a Democrat, then as an independent.

Initially, Lieberman was hailed as a canny choice with allies on both sides of the aisle, but then Senate Minority Leader Chuck Schumer, D-N.Y., argued against the employment of a “career politician” of either party to lead the FBI.

Before Lieberman became the leading candidate, the list of possible directors included former NYPD Commissioner Ray Kelly, former House Intelligence Committee Chairman Mike Rogers, R-Mich., who was endorsed by the FBI Agents Association; Acting FBI Director Andrew McCabe; Mayor of Colorado Springs John Suthers; former federal appellate court judge and current Boeing executive John Luttig; Director for the FBI’s Criminal, Cyber, Response and Services Branch Paul Abbate; Associate Judge for the New York Court of Appeals Mike Garcia; and Larry Thompson, former deputy attorney general under President George W. Bush.

The White House did not immediately respond to Fox News’ request for comment as to whether any of these candidates are still under consideration.

Fox News' John Roberts, Nick Kalman, Serafin Gomez contributed to this report.