Sen. Cory Booker slammed President Trump's pick of Brett Kavanaugh to replace Anthony Kennedy on the Supreme Court, calling the selection "self-serving."

Trump on Monday nominated the District of Columbia Court of Appeals judge to fill the impending vacancy of retiring Justice Anthony Kennedy.

Appearing on MSNBC, Booker (D-N.J.) said that the president chose the one person who would assuredly rule in his favor if the Russia investigation made its way to the Supreme Court.

"He picked the one guy who has specifically written that a president, in fact, should not be the subject of a criminal investigation, which the president is right now," Booker said.

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Booker called Kavanaugh "the most self-serving person" Trump could have chosen in order to protect himself.

"I'm a little, sort of, stunned at the way this has all played out," he said.

Trump's selection was, as expected, met with widespread criticism by Democrats, including Sen. Jeff Merkley (Ore.) who called the pick "unacceptable."

Fox News politics editor Chris Stirewalt said Tuesday on "America's Newsroom" that the article Booker was referring to was Kavanaugh's 2009 piece in the Minnesota Law Review in which Kavanaugh said former federal judge Ken Starr's investigation into former President Bill Clinton was a mistake.

Kavanaugh's piece seemed to suggest that he believed a president could not be sued or investigated while in office.

"That was Kavanaugh calling himself out, essentially," Stirewalt said.

Kavanaugh had written that he believes it's "vital that the President be able to focus on his never-ending tasks with as few distractions as possible.”

He said that criminal investigations and lawsuits should be deferred until a president is out of office.

“Even the lesser burdens of a criminal investigation – including preparing for questioning by criminal investigators – are time-consuming and distracting. Like civil suits, criminal investigations take the President’s focus away from his or her responsibilities to the people,” he said. “And a President who is concerned about an ongoing criminal investigation is almost inevitably going to do a worse job as President.”

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