Utah Sen. Mike Lee joined Judge Andrew Napolitano Monday on Fox Nation's "Liberty File" to discuss how far senators can go in examining a judicial nominee's religious beliefs.

Lee (R) challenged Hawaii Sen. Mazie Hirono (D) last week in a Senate Judiciary Committee hearing over her party's questioning of Neomi Rao, President Trump’s nominee to replace Supreme Court Justice Brett Kavanaugh on the U.S. Court of Appeals for the D.C. Circuit.

Specifically, New Jersey Sen. Cory Booker repeatedly asked Rao if she believed gay relationships were "immoral" or a "sin."

"I would ask Sen. Hirono in what circumstance -- in what way, shape, or form -- is asking Neomi Rao whether she believes particular conduct to be sinful an appropriate question to be asked in this committee. Ever," Lee said.

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Napolitano asked Lee on Monday if Democrats can be expected to intrude into nominees' religious views simply because they outwardly express them.

"I certainly hope not," Lee replied. "The minute you open up the door to this, you're opening up a Pandora's Box. This is just a very bad idea."

He said that once questions are raised about what a judicial nominee believes to be a sin, it "cuts against believers."

"[It] ... could be perceived as a non-believer's way of ridiculing religious belief itself," he said. "That's very problematic and I think most Americans would have a problem with that as well."

Napolitano also cited Sen. Dianne Feinstein's questioning of then-professor Amy Coney Barrett about her Roman Catholic faith during her Court of Appeals confirmation hearing.

Feinstein (D-Calif.) said during the 2017 hearing that "the dogma lives loudly within" Barrett and suggested that her strong beliefs made her unfit for the bench.

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