For the first time, a sitting Senator will testify against another sitting Senator when Cory Booker (D-NJ) appears before the Judiciary Committee during Jeff Sessions’ (R-AL) nomination hearing for Attorney General.

Booker explained his remarkable decision to MSNBC’s Chris Hayes:

.@CoryBooker will testify against his colleague @SenatorSessions: "These are extraordinary times" #inners https://t.co/7uhCLf8PaX

— All In w/Chris Hayes (@allinwithchris) January 10, 2017

HAYES: Concretely, does that mean, for instance, voting against Jeff Sessions, your former colleague? Does that mean pushing the Democratic leadership team to demand these thirty hours, to try to extend the process? What does it mean concretely?

BOOKER: Well, concretely, I’m breaking a pretty long Senate tradition by actually being a sitting Senator testifying tomorrow against another sitting Senator. So, please understand, I think these are extraordinary times and they call for extraordinary measures.

HAYES: You’ll be testifying against your former colleague Jeff Sessions tomorrow in that hearing?

BOOKER: I’ll be testifying against my current colleague, either tomorrow or Wednesday.

Booker further noted: “We’ve seen Jeff Sessions — that’s Senator Jeff Sessions — consistently voting against or speaking out against key ideals of the Voting Rights Act, taking measures to try to block criminal justice reform. He has a posture and a positioning that I think represent a real danger to our country.”

Several members of the Congressional Black Caucus, including civil rights leader Rep. John Lewis (D-GA), will also be testifying against Sessions, though the Republican chair of the Senate Judiciary Committee, Senator Chuck Grassley (R-IA), has reportedly said he will only let them testify at the end of the hearing.

Interim DNC Chair Donna Brazile explained in a statement why the resistance to Sessions’ nomination is so important to Democrats:

As our nation’s top law-enforcement officer, the U.S. Attorney General bears a sacred responsibility to fight injustice and defend the defenseless. Senator Sessions’ extreme views are directly at odds with the mission of the office he seeks.

Over the course of his career he has called protections for people with disabilities ‘dangerous’ and unnecessary. He has fought against women’s rights and women’s equality, voting against paycheck fairness, the Violence Against Women Act, voting to defund Planned Parenthood, and questioning the constitutional legitimacy of Roe V. Wade. He said he does not believe that grabbing women by their genitals against their consent is sexual assault.

Sessions has fought against voting rights and celebrated the gutting of the Voting Rights Act, which he called ‘intrusive.’ He helped block reforms in prison sentencing, attacked civil rights activists in court, and has a long history of making discriminatory and racially charged remarks. He has fought against LGBT rights, voting against the Employment Non-Discrimination Act to allow workplace discrimination based on sexual orientation. He even likened his effort to ban same-sex marriage to the movement to abolish slavery.

Sessions is worse than unqualified for the job – he stands for everything our Attorney General should be fighting. Still more troubling is the fact that the Senate is rushing to hold this and other confirmation hearings before the Office of Government Ethics has finished reviewing the candidates’ financial and ethics information, increasing the likelihood that they could be compromised by their business ties or personal past.

Thirty years ago, the Senate rejected Sessions’ appointment to a federal judgeship because he was deemed too extreme then. If they confirm him now, Republicans will be turning back the clock on all the progress we’ve made as a nation. Donald Trump could not have nominated a worse candidate.