Washington (CNN) Three potential 2020 presidential candidates went on the attack against President Donald Trump -- and previewed their own agendas -- on Tuesday in the Senate Judiciary Committee's confirmation hearing for Trump's nominee for attorney general, William Barr.

California Sen. Kamala Harris questioned the effectiveness of Trump's calls for a border wall. New Jersey Sen. Cory Booker grilled Barr on racial inequalities in the criminal justice system. And Minnesota Sen. Amy Klobuchar pressed Barr on Trump's attacks on news organizations.

With Republicans holding a Senate majority, Barr's confirmation is all but certain. Still, the hearing showcased how the 2020 Democratic presidential race is playing out in high-profile moments in the Senate -- much like Barack Obama and Hillary Clinton used Senate hearings as anti-Iraq war launchpads 12 years earlier.

Klobuchar highlighted Trump's attacks on journalists. She also pointed to the death of Washington Post journalist Jamal Khashoggi in a Saudi Arabian consulate in Turkey.

"If you're confirmed, will the Justice Department jail reporters for doing their jobs?" Klobuchar asked.

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