Sen. Cory Booker at the Democratic National Convention in Philadelphia on July 25, 2016
ROBYN BECK/AFP/Getty Images

Sen. Cory Booker (D-N.J.) will testify Wednesday against Jeff Sessions' nomination to become U.S. attorney general, making Booker the first sitting senator to oppose another sitting senator for a Cabinet position.

With Democrats scrambling for fresh, new leadership, many Republicans believe that Booker's move is political jockeying for a national platform to serve his own interests, since Booker's name is one of those mentioned for presidential consideration in 2020, CNN reports.

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Sen. Tom Cotton (R-Ark.) took to Facebook to question Booker's motives, calling the move a "disgraceful breach of custom."

"This hearing simply offers a platform for his presidential aspirations. Sen. Booker is better than that, and he knows better," Cotton wrote.

According to CNN, Democrats have also made clear that Booker's decision to testify is a solo effort.

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

Booker told CNN on Tuesday that he had had a call to conscience.

"I do not take lightly the decision to testify against a Senate colleague," Booker said. "But the immense powers of the attorney general, combined with the deeply troubling views of this nominee, is a call to conscience.

"This is one of the more consequential appointments in American history right now, given the state of a lot of our challenges we have with our policing, a lot of challenges we have with race relations, gay and lesbian relations," Booker said, CNN reports.

Read more at CNN.