Story highlights Liberals are searching for new leadership within their party

Jeff Sessions' 1986 nomination for a judgeship was derailed over accusations of racism

Washington (CNN) Sen. Cory Booker will make history Wednesday when he becomes the first sitting senator to testify against another sitting senator for a Cabinet post as he fights Jeff Sessions' nomination to become President-elect Donald Trump's attorney general.

The decision has thrust Booker, a New Jersey Democrat and fixture on lists of potential 2020 presidential candidates, into the limelight.

Republicans quickly accused Booker of seeking to improve his own political prospects.

Democrats made clear Booker is on his own.

"It's not for me to approve or disapprove. He's asked to testify and his message is whatever he wants it to be," said Sen. Dick Durbin of Illinois, the No. 2-ranking Democrat.

Read More