Historian and author James Simon said in an interview that aired Tuesday on "Rising" that President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE probably has not read the opinions of his Supreme Court picks, Judge Brett Kavanaugh and Justice Neil Gorsuch.

"Without showing disrespect, I suspect that President Trump has not read any of the opinions of Gorsuch or Kavanaugh, but you can be very sure that his advisers, who are advising him on judicial appointments, have, and they know exactly where these judges stand on important issues," Simon told Hill.TV's Krystal Ball.

Simon's book "'Eisenhower Vs. Warren: The Battle for Civil Rights and Liberties" details the feud between former President Eisenhower and his Supreme Court pick Chief Justice Earl Warren over the issue of civil rights.

Simon said former administrations did not vet their high court picks nearly as much as presidents do today, which resulted in ideological differences between presidents and judges they appointed.

"Eisenhower really later said, and he said it in private not in public, that he thought appointing Warren was a really big mistake, and there are others later that had fooled or surprised the presidents who appointed them," Simon said.

"You can think in more recent years John Paul Stevens was appointed by the Republican President Ford and became quite liberal. Harry Blackmun, appointed by President Nixon, became quite liberal. David Souter appointed by the first President Bush became quite liberal. These days, however, that's less likely to happen because of our polarized political climate. The people advising the president tend to vet the potential candidates very, very carefully," he continued.

His comments come as Kavanaugh faces several obstacles in his confirmation process amid two sexual assault allegations against him.

Kavanaugh and one of his accusers, Christine Blasey Ford, are set to testify before the Senate Judiciary Committee on Thursday.

Trump has publicly expressed his support for Kavanaugh, who has denied the allegations.

— Julia Manchester