Jessie Liu , U.S. attorney for the District of Columbia, speaks to President Trump last month during a White House meeting about border security. (Jabin Botsford/The Washington Post)

President Trump plans to nominate the U.S. attorney for the District of Columbia., Jessie K. Liu, to become the Justice Department’s No. 3 official, the White House announced Tuesday.

If confirmed, Liu would assume the job of associate attorney general and her principal responsibility would be overseeing the Justice Department’s civil litigation.

Liu, 46, was confirmed in August 2017 to head the country’s largest U.S. attorney’s office, one that often oversees politically sensitive investigations of the executive and legislative branches.

It has been more than a year since the last associate attorney general, Rachel Brand, left that post — an unusually long period for such a senior position to lack even a nominee.

Last month, Trump said he planned to nominate a Transportation Department official, Jeffrey Rosen, to take the job of deputy attorney general currently held by Rod J. Rosenstein.

The selections of Rosen and Liu would put in place a new trio of senior officials running the Justice Department, now led by newly confirmed attorney general William P. Barr, who previously served as attorney general during the George H.W. Bush presidency.

“Jessie has distinguished herself as a first-class attorney in private practice, in the Treasury Department, and in five different positions over her career at the Department of Justice,” Barr said in a statement, adding that he was pleased to recommend Liu and grateful for her nomination.

When Trump nominated Liu to become U.S. attorney in 2017, some Democrats questioned why he had met with her in person before the nomination, a departure from standard practice in previous administrations. Nevertheless, Liu’s nomination did not generate much controversy, and she has been seen as a steadying presence at a U.S. attorney’s office whose 300 attorneys have unique federal jurisdiction in the nation’s capital to prosecute local and federal crimes.

She reorganized an office where her recent predecessors were criticized for their handling of a drawn-out public corruption investigation of then-D.C. Mayor Vincent C. Gray (D), who was never charged but was voted out of office after prosecutors disclosed, in an pre-election news conference, that he was their target.

Liu’s highest-profile move as U.S. attorney came last month, when her office began to prosecute more District defendants for gun and drug crimes in federal rather than local court, as the city struggles with a 40 percent spike in homicides.

Liu, a graduate of Yale Law School, was an assistant U.S. attorney in the District from 2002 to 2006 before joining the Justice Department’s national security division and serving as a deputy assistant attorney general with the civil rights division until 2009.

She also worked at the Morrison & Foerster and Jenner & Block law firms.