As stained coffee cups and empty takeout containers pile up on the National Mall in Washington, D.C., and Donald Trump points fingers at the Democrats, Nancy Pelosi has been quietly preparing to assume her role as the president’s chief antagonist. During the reprieve between Christmas and the New Year, the California lawmaker announced the appointment of Justice Department veteran Doug Letter as the new general counsel for the House of Representatives. Though Pelosi’s decision was met with little fanfare, Letter will be the linchpin in the oversight nightmare that House Democrats are preparing for Trump and his administration, circa tomorrow. “It is fanciful to think that there won’t be a substantial oversight function served by the new House. There are just so many issues that have gone without scrutiny,” Robert Loeb, a D.C. appellate lawyer, told me. It will be Letter’s job to inform Pelosi and other lawmakers “what their options are and what the risks and costs are” when it comes to leveraging Congress’s oversight authority.

Democrats have not been coy about their plans to exhume the scandals their Republican colleagues buried during the first two years of Trump’s presidency. As I previously reported, House Democrats have been treating January 3—the day Pelosi takes the gavel from Paul Ryan—like D-Day, with teams of staffers already lined up to open investigations into the president’s deputies, associates, and businesses. The anticipated lines of inquiry run the gamut—child separation at the border; Trump-Russia collusion; the F.B.I. investigation into the sexual misconduct allegations against Supreme Court Justice Brett Kavanaugh; White House security clearances; emoluments; the list goes on. And regardless of the specific rabbit holes that House Democrats choose to go down, protracted federal court battles seem assured. As general counsel, Letter would be the point person in any litigation brought on behalf of Pelosi and the House.

To former colleagues, Letter seems poised for the challenge. “For the last dozen years, I’ve litigated against Doug and with him at my side in some of the most consequential appeals in our lifetimes. Every time, he has been brilliant, professional, nonpartisan, and balanced,” Neal Katyal, who served as acting solicitor general at the Justice Department under Barack Obama, told me. “There is no one more experienced, and no one better suited to this job.” Letter has signaled as much, himself. “I am eager to apply my litigation experience as I take on the challenges and opportunities that come with the important position,” he said in a statement about his appointment.

Letter, after all, has spent decades fighting on the other side of the Congressional Oversight battle, giving him unmatched insight into all the ways the Trump administration could maneuver to block House Democrats in court. In February, after 40 years at the Justice Department, he retired as the director of the appellate staff in the civil division, where he was frequently on the receiving end of congressional investigations and other assorted fishing expeditions. “Doug has defended against subpoenas and against attempts from Congress to coerce things from the executive branch. Doug knows those arguments and those legal doctrines better than anyone,” said Loeb, who worked alongside Letter for decades at the Justice Department. “He will be a great wealth of wisdom in providing advice to not just Pelosi as speaker and representatives in the House but also giving advice to all the committee chairs.”

David Laufman, a former federal prosecutor who overlapped with Letter at Justice, elaborated on the sentiment. “Doug will provide an unimpeachably objective source of legal counsel about the substantive merits or liabilities associated with pursuing oversight that can result in litigation in the federal courts. He and his team will help explain to committee chairmen who might otherwise have a hair trigger in issuing subpoenas what the litigation roadmap will look like to enforce compliance where you have recalcitrant recipients of those subpoenas,” he told me. “He will be a formidable opponent for anyone who chooses to litigate against the House in the federal courts.”