A Republican U.S. senator who could be pivotal in determining whether President Donald Trump's nominee Brett Kavanaugh gets to sit on the Supreme Court raised concerns on Tuesday about the judge's "partisan" tone at last week's hearing into sexual misconduct allegations.

As the FBI completed interviews with four people as part of its one-week investigation into the allegations against Kavanaugh, moderate Republican Sen. Jeff Flake said he was worried about the conservative federal appeals court judge's performance before the Senate Judiciary Committee last Thursday.

"I was very troubled by the tone of the remarks. ... The interaction with the members was sharp and partisan, and that concerns me," Flake said.