Alarm bells understandably rang earlier this month when Matthew G. Whitaker, the chief of staff to fired Attorney General Jeff Sessions, leapfrogged over more senior — and Senate-confirmed — Justice Department officials to become President Donald Trump’s acting attorney general.

It’s hard to imagine a less reassuring replacement. As a commentator, Whitaker (a former U.S. attorney in Iowa) had questioned the investigation conducted by special counsel Robert Mueller and even suggested that Mueller’s appointment smelled “a little fishy.” Yet as acting attorney general, Whitaker is positioned to be the ultimate overseer of an investigation that, among other matters, is looking into whether Trump’s 2016 campaign illegally colluded with Russia.

Even more ominously, Trump seems to be in no rush to nominate a new attorney general. Meanwhile, he said that he “would not get involved” if Whitaker moved to curtail Mueller’s investigation. That’s hardly surprising, given that Trump has described the probe as an illegal “witch hunt.”

Trump’s latest comments underline the importance of enacting legislation to protect Mueller, which Senate Majority Leader Mitch McConnell, R-Ky., perversely has refused to advance despite its bipartisan backing. The Special Counsel Independence and Integrity Act approved by the Senate Judiciary Committee in April would codify a Justice Department rule that special counsels can be fired only for good cause and would allow a counsel to appeal his or her dismissal in court. It needs to be enacted.

But Trump’s comments, including his praise for Whitaker, point to another problem: By elevating Whitaker, who is not a Senate-confirmed official, the president is violating the spirit and possibly the letter of the Constitution’s Appointments Clause. In a lawsuit filed last week, three Democratic U.S. senators — Richard Blumenthal of Connecticut, Mazie K. Hirono of Hawaii and Sheldon Whitehouse of Rhode Island — claim that Whitaker’s appointment flouts not only the Constitution but also a statute setting out a line of succession for the Justice Department.

Installing a staffer like Whitaker as acting attorney general would be troubling under any circumstances. But with the president’s own conduct being scrutinized by Mueller, it’s vital that an official confirmed by the Senate have oversight over the probe.

Because Sessions rightly had recused himself from the Russia investigation in light of his role in the 2016 Trump campaign, that oversight had been provided by Session’s Senate-confirmed deputy, Rod Rosenstein, who appointed Mueller. But with Sessions’ forced resignation, that authority passes to Whitaker.

Sen. Lindsey Graham, R-S.C., who is expected to chair the Senate Judiciary Committee in the new Congress, blithely declared that he didn’t see “any indication at all” that Trump or Whitaker will interfere with Mueller’s investigation.

Pardon us if we’re not reassured.