New Jersey Sen. Cory Booker will break longstanding Senate tradition on Wednesday by testifying against his colleague, Alabama Sen. Jeff Sessions, during the Republican’s Senate confirmation hearing for attorney general.

Booker will join two other Democratic lawmakers, Georgia Rep. John Lewis and Louisiana Rep. Cedric Richmond, for the high-profile Senate Judiciary Committee hearing.

Booker’s move is believed to be the first time that a sitting senator has testified against a colleague during a cabinet nomination hearing.

“These are extraordinary times, and they call for extraordinary measures,” Booker said of his decision during an interview with MSNBC’s Chris Hayes on Monday.

Booker, who also plans to vote against Sessions, criticized the Republican’s positions on criminal justice reform, civil rights, voting rights and hate crime legislation.

“He has a posture and positioning that I think represent a real danger to our country,” said Booker.

Democrats have been heavily critical of President-Elect Donald Trump’s pick of Sessions. A former U.S. attorney, Sessions is deeply conservative on criminal justice issues and immigration.

Booker, who many believe has his eye on a 2020 presidential bid, made a point in his interview Monday to let Hayes know how unprecedented his testimony will be.

“Concretely, I’m breaking a pretty long Senate tradition by actually being a sitting senator testifying against another sitting senator,” said Booker.

When Hayes mistakenly said that Sessions was a former senator, Booker corrected the host.

“I’ll be testifying against my current colleague,” he said.

Booker also remarked on Twitter about the historical significance of his testimony.

Ohio Sen. Sherrod Brown announced last week that he will vote against Sessions for attorney general, becoming the first Democrat to do so.

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