Acting attorney general Matthew G. Whitaker, center, and Labor Secretary Alexander Acosta, right, attend a wreath-laying ceremony at the Tomb of the Unknown Soldier in Arlington National Cemetery on Sunday. (Andrew Harnik/AP)

Adam B. Schiff, a Democrat, represents California’s 28th District in the House, where he is the ranking minority member of the Intelligence Committee.

Only hours after the magnitude of Democratic gains in the House became apparent, President Trump ousted Attorney General Jeff Sessions, putting special counsel Robert S. Mueller III’s investigation in imminent danger. This represents the president’s most direct challenge yet to the rule of law.

Instead of elevating Deputy Attorney General Rod J. Rosenstein, the most senior Senate-confirmed officer at the Justice Department, Trump circumvented normal succession by handpicking Matthew G. Whitaker, Sessions’s chief of staff and a person who has publicly criticized the special counsel’s investigation and has troubling conflicts of interest.

The president and Whitaker should heed this warning: The new Democratic majority will protect the special counsel and the integrity of the Justice Department. Should Whitaker fail to recuse himself — all indications are that he plans not to — and seek to obstruct the investigation, serve as a back channel to the president or his legal team or interfere in the investigations in any way, he will be called to answer. His actions will be exposed.

It is no mystery why the president chose Whitaker, an obscure and ill-qualified official never confirmed by the Senate, which many legal experts believe makes the appointment itself unconstitutional. Trump chose him to protect himself, his family and his close associates from the special counsel’s investigation and other investigations within the Justice Department.

Though I had many profound disagreements with Sessions, he was correct to follow the rules meant to ensure public confidence in the fair administration of justice and recuse himself, even though the president viewed Sessions’s compliance as a singular act of disloyalty. We must demand the highest ethical standards of everyone at the Justice Department, including the attorney general.

There is no indication that Whitaker has likewise consulted with ethics officials, as his past public statements, associations and the manner of his appointment make clear that he should have no role in overseeing the special counsel’s investigation or any matter related to the president and his campaign.

It’s highly likely that Trump elevated and appointed Whitaker in the first place because of his open hostility to the special counsel. Whitaker has not only been publicly critical of Mueller but also suggested starving his office of funds and suggested that the special counsel should be prohibited from investigating the president’s finances. If the Russians possess financial leverage over the president — and there are credible allegations they may have laundered money through the Trump businesses — it would be negligent to our national security not to find out.

Whitaker also has strong ties to the Trump campaign. In 2014, he chaired Sam Clovis’s campaign for Iowa state treasurer. Clovis went on to serve as national co-chairman of Trump’s presidential campaign, and reportedly has testified before a grand jury in the special counsel’s investigation.

All this demands Whitaker’s immediate recusal. If he does not recuse himself, Whitaker could seek access to the special counsel’s plans and evidence, including grand jury testimony, and would be in a position not just to funnel information to Trump and his legal defense team but also to abuse his authority to cripple or end the investigation. Whitaker could attempt to prevent evidence from reaching Congress and the public or stop the special counsel from subpoenaing important testimony, including from Trump himself.

Since the special counsel was appointed, Democrats in Congress have called on Republicans to pass legislation to protect the investigation from interference. The Senate Judiciary Committee approved such a bill on a bipartisan basis. And yet we were repeatedly informed that such legislation was “ not necessary,” despite the president’s clear determination to protect himself at all costs and even as prosecutors obtained guilty pleas and convictions from the president’s campaign chairman, deputy campaign chairman, former national security adviser, foreign policy adviser and personal attorney. Even now, Senate Majority Leader Mitch McConnell (Ky.) professes no need to protect the Mueller investigation.

Congressional Democrats have written to the department’s top ethics official, outlining the obvious case for recusal and seeking information about any ethics guidance given to Whitaker on the matter. Separately, Democrats in the House and Senate have demanded that all relevant documents across the U.S. government related to that investigation, and Sessions’s termination, be preserved. Congress should likewise ensure that any Justice official overseeing the probe publicly pledge to protect the integrity of the special counsel. We will also revive legislation designed to protect Mueller from any interference or firing not based on good cause.

Trump, and those who would abet him in undermining the independence of the Justice Department, should understand this: The truth will come out.

After his firing by President Richard M. Nixon, former Watergate special prosecutor Archibald Cox said the question of “whether ours shall continue to be a government of laws and not men is now for Congress and ultimately the American people.” With this latest, unprecedented action, Trump has put Cox’s question once more squarely before the people’s representatives. We must answer it by acting as a coequal branch of government and defending the rule of law.