Attorney General Jeff Sessions resigned at the president’s request on Wednesday — and Democrats immediately moved to protect special counsel Robert Mueller’s investigation.

Democrats sent at least nine letters to Trump administration officials — including new acting Attorney General Matthew Whitaker — requesting that the White House, Justice Department, and other agencies preserve “all materials related to any investigations by the Special Counsel’s office” and to Sessions’s departure.

Incoming House Judiciary Chair Jerrold Nadler (D-NY), incoming House Oversight and Government Reform Chair Elijah Cummings (D-MD), and incoming House Intelligence Chair Adam Schiff (D-CA) — along with Senate Judiciary Committee ranking member Dianne Feinstein (D-CA) — all signed the letters.

“Preservation of records is critical to ensure that we are able to do our work without interference or delay,” they wrote, adding that they’ll be investigating Sessions’s departure.

The Democrats addressed these letters to a wide swath of Trump officials — not all of whom are obviously connected to special counsel Robert Mueller’s investigation into Russian interference in the 2016 election. They include:

FBI Director Chris Wray

White House counsel Pat Cipollone

Director of National Intelligence Dan Coats

CIA Director Gina Haspel

Deputy US Attorney for the Southern District of New York Robert Khuzami

Treasury Secretary Steve Mnuchin

National Security Agency Director Paul Nakasone

IRS Commissioner Charles Rettig

The letters are simply asking these officials to save records, but it lays the foundation for future document requests that House Democrats can pursue when the new majority arrives in January. Democrats in charge of committees will be able to launch investigations that are backed by the power to subpoena records or in-person testimony.

Incoming House Democratic leaders have made it clear that they want a more robust investigation into Russian interference and the 2016 election, and to find out more about President Trump’s tax returns. These letters indicate that they’ll also keep following Mueller’s line of inquiry and examine Sessions’s resignation.

The letters can’t compel the administration officials to do anything — at least not yet. But they’re the first step in launching any type of future investigation.

What do Democrats hope these letters will achieve?

It may seem a little premature, even risky, for Democrats to let the Trump administration know which investigations they’re lining up, even before all the midterm election votes have even been counted.

To be clear, Sessions’s ouster after the midterms seemed all but assured. Trump saw Session’s decision to recuse himself from the Russia investigation as the ultimate betrayal, and he frequently blasted his “beleaguered” attorney general. The political consequences of pushing out Sessions restrained Trump, especially before the 2018 elections.

But less than 24 hours after the polls closed, Trump asked Sessions to go. And the president’s decision to go outside the Justice Department succession order and install a Trump loyalist as acting attorney general raises serious questions. Whitaker is expected to take full control of the Mueller investigation, and his past comments put the fate of the special counsel’s probe in doubt.

Democrats, then, are anticipating that Sessions’s resignation, and its consequences, will have ripple effects far beyond this week. They’re letting the administration know that if Mueller’s probe is curtailed or shutdown, House Democrats will not let this go unanswered.

This marks a reversal from the past year, when Trump’s Republican allies in the House besieged Deputy Attorney General Rod Rosenstein, who’d been overseeing the Mueller probe, with a multitude of document requests related to the FBI’s investigation into Trump campaign aides’ Russia ties and Hillary Clinton’s use of a private email server.

It resulted in a months-long showdown, with House members claiming Rosenstein was stonewalling requests. They even introduced articles of impeachment against the deputy AG, though the attempt was quickly dropped.

At the time, House Republicans’ gambit served to highlight the bizarre dynamics of the Trump era — members of the presidents’ own party waging war against a Trump appointee who was investigating Trump’s campaign.

With Democrats in charge in the House, though, things will probably follow a more typical playbook: an opposition party investigating the president in power. And that, it seems, is already beginning.