Biden’s Choice for Justice Dept.’s No. 2 Is Lisa Monaco

Ms. Monaco has a reputation for working and preparing relentlessly. She is even-tempered and exhibits a quiet, firm confidence, even under pressure, friends and former colleagues said. She does not raise her voice. Friends called her funny and warm and self-deprecating in the face of praise. When a fellow department alumnus took note of her remarkable career, she replied, “I’ve been very, very lucky.”

As Mr. Obama’s homeland security adviser, she presided over decisions with difficult operational, policy and legal dimensions, and they often involved military action. A disagreement or a provocative question could derail hours of work, and it could be hard to get people back on track, former colleagues said.

“She was a lawyer at a table with military leaders. She had to earn their respect and lead them toward the conclusion that was consistent with what the president wanted from the process,” Mr. Olsen said. “She was able to pull that off time and time again.”

“Her trial lawyer experience in D.C. superior court likely served her well,” Mr. Olsen said. “Not everything will go as planned. Your police officer won’t show up to testify and you have to keep a poker face before the jury. You manage her way through that by keeping calm and appealing to people’s better natures. I’ve seen her do that in the Situation Room” at the White House.

In 2013, the Boston Marathon bombing tested her skills and resolve. The attack happened in Ms. Monaco’s hometown as her brother stood among the crowd, cheering on the runners.

Her knowledge of domestic extremism and the workings of the government, her work ethic and her ability to corral colleagues were crucial to helping the Obama administration respond, Mr. Olsen said.

Reflecting on the Boston Marathon bombing, Sept. 11 and other national security challenges, Ms. Monaco warned in 2016 that “the terrorist threat has evolved, and it’s done so dramatically.”

“It is broader, more diffuse and less predictable than at any time since 9/11,” she said at an event hosted by the Council on Foreign Relations. “Terrorism today is increasingly defined by small cells or lone actors, sometimes with little or no direct contact with terrorist organizations. Those people have succumbed to violent extremism.”