Speaker-designate Nancy Pelosi, D-Calif., has picked a new guiding force for Democrats investigating and potentially impeaching President Trump when they take control of the House next year.

Douglas Letter, a 40-year veteran of the Justice Department and former associate counsel in President Bill Clinton's White House, will be appointed to the role of House general counsel, Pelosi said in a statement.

“Douglas Letter has an outstanding and highly decorated record of achievement in service of America,” Pelosi said. “He will bring deep experience and legal expertise to the House, as he counsels and represents our institution, Members and staff as House General Counsel.”

Letter, 65, served as director of the Justice Department's Civil Division appellate staff up until February — a departure that was facilitated, sources told NPR, because of Trump's constant criticisms of the DOJ.

He wrote in September it was "worrying" that Trump's lawyer Rudy Giuliani had suggested the use of executive privilege to bury Mueller's report at the conclusion of his investigation. He said this assertion seemed "premature and misplaced."

Letter's long career for the DOJ included roles such as deputy associate attorney general under former Attorney General Janet Reno, and senior counselor to former Attorney General Eric Holder. His decades of service, which included working on cases such as Obergefell v. Hodges, the 2015 landmark case which legalized gay marriage, was praised by the likes of Holder and Benjamin Wittes, editor-in-chief of Lawfare and friend to ex-FBI Director James Comey.

"This is a very big deal — and a very sad thing. Doug Letter has run this office for a long time. He is an institution guy who has represented administrations of both parties through some of their toughest litigations. It says worlds that he won’t be representing this one any more," Wittes tweeted earlier this year.

His going-away party was attended by Supreme Court Chief Justice John Roberts and Justice Neil Gorsuch. Since then, he has been working at the Institute for Constitutional Advocacy and Protection at the Georgetown University Law Center.

In his new role, Letter will provide legal advice to lawmakers and their staff, regardless of political affiliation, according to the Office of General Counsel website. That means Letter is poised to be at the heart of any debate over impeaching the president.

Democrats poised to take control of committees in January have said they are ready to begin a bevy of investigations into the president and a number of members have called for Trump's impeachment. In the run-up to the November midterm elections, Pelosi indicated that wasn't poised to seek impeachment if her party won power. But she didn't dismiss the prospect either.

"It depends on what happens in the [special counsel Robert] Mueller investigation, but that is not unifying and I get criticized in my own party for not being in support of it," Pelosi said to PBS in November. "But I'm not. If that happens, it would have to be bipartisan, and the evidence would have to be so conclusive."

Letter will replace the current general counsel, Thomas Hungar, who began the job in 2016, in January.

“I look forward to serving the interests of the House of Representatives and its Members,” Letter said. “I am eager to apply my litigation experience as I take on the challenges and opportunities that come with the important position of House General Counsel.”

His hiring was heralded by some members of the media as being a big deal and cheered by some of the anti-Trump crowd.

"Kudos to ⁦@GeorgetownICAP⁩’s brilliant Doug Letter on his appointment as the general counsel of the House. I litigated my very first appellate case against him almost a quarter of a century ago—a masterful lawyer and a mensch to boot," tweeted Norman Eisen, a one-time Obama White House ethics lawyer and chairman of Citizens for Responsibility and Ethics in Washington.