Top congressional Democrats say the Trump administration has misread federal law to justify the appointment of acting Attorney General Matt Whitaker and therefore put forward a "fatally flawed" rationale for putting him in that position.

Senate Judiciary Committee ranking member Dianne Feinstein, D-Calif., House Judiciary Committee ranking member Jerry Nadler, D-N.Y., and House Intelligence Committee ranking member Adam Schiff, D-Calif., said the Office of Legal Counsel opinion released Wednesday is “fatally flawed” because it relies “exclusively" on the Vacancies Reform Act, while also and “twisting the plain language of the Constitution.”

They said Deputy Attorney General Rod Rosenstein should have been named automatically to replace Jeff Sessions, who was fired last week.

“First, there’s already a statute that lays out what should happen when the attorney general’s position becomes vacant: the Justice Department’s own succession law, which authorizes the deputy attorney general to exercise the attorney general’s powers and provides for a line of Senate-confirmed successors if the deputy attorney general is unable to exercise the attorney general’s duties. This specific statute’s language should prevail over the more general provisions of the Vacancies Reform Act," the Democrats wrote.

Rather than appoint Rosenstein, Trump invoked a provision in the Federal Vacancies Reform Act to appoint Whitaker, and a memo from the Justice Department's Office of Legal Counsel upheld Whitaker's temporary role leading the department.

Democrats also argued that the Senate needs to appoint the acting attorney general.

[Opinion: The Senate shouldn't be sleeping on Whitaker's unconstitutional appointment]

“Second, the Constitution requires that any principal officer must be confirmed by the Senate. OLC itself could uncover only one case in which an individual who wasn’t Senate confirmed ever served as acting attorney general, and that was for six days in 1866 — the year after the Civil War ended, four years before the Justice Department’s founding and a century before the DOJ succession law was enacted," the Democrats said.

"For more than a century, the executive branch has understood, and Congress has agreed, that the attorney general, including one serving in an acting capacity […] must be nominated by the president and confirmed by the Senate,” they added.

The Justice Department opinion said Whitaker could be installed as acting attorney general under the Vacancies Reform Act because “he had been serving in the Department of Justice at a sufficiently senior pay level for over a year.”

The law allows the president to use the law to "depart from the succession order specified” under a Justice Department succession statute, the opinion said.

The opinion added that Whitaker’s designation is consistent with the Appointments Clause of the Constitution, because while the attorney general is a position that requires Senate confirmation, “someone who temporarily performs his duties is not.”

In a call with reporters, a senior Justice Department official pointed out that the U.S. has an extensive history of non–Senate-confirmed individuals taking on “acting” roles. When putting together the memo, the OLC found more than 160 such examples throughout the country's history. The official and the OLC memo both noted that in 1866, there was an acting attorney general appointed by former President Andrew Johnson who had not previously been confirmed by the Senate.

Feinstein, Nadler, and Schiff are the first Democratic lawmakers to come out publicly against the OLC opinion since its release Wednesday morning. They accused Trump of bypassing Congress to “embed a political operative to serve his own interests.”

Congressional Democrats, including a swath of incoming House committee chairs once the party takes the majority in early January, have criticized Whitaker's appointment as acting attorney general. In 2017, Whitaker made comments questioning and at times criticizing Mueller’s ongoing probe.

“There should be bipartisan concern that this will embolden the future use of temporary appointments for illegitimate purposes. That’s not what the framers or Congress intended," Feinstein, Nadler, and Schiff said. "The attorney general must be Senate confirmed, plain and simple. This can’t be allowed to stand.”

When House Democrats take over the majority in January, a handful of incoming committee chairmen have already said they plan to call Whitaker to testify.