US Supreme Court nominee Neil Gorsuch is expected to face tough scrutiny at his Senate confirmation hearing.
Democrats will seek to make the case that he is a pro-business, social conservative insufficiently independent of President Donald Trump.
In a bid to place hurdles in the way of Mr Gorsuch's expected confirmation by the Republican-controlled Senate, Democrats on the judiciary committee considering the nomination have said they will probe him on several fronts based mainly on his record as a federal appeals court judge and a Justice Department appointee under former president George W Bush.
Nominated by Mr Trump to fill a year-old vacancy on the court, Mr Gorsuch is a conservative appeals court judge from Colorado. He is expected to try to engage senators without being pinned down on specifics.
Among questions Mr Gorsuch will face will be whether he is sufficiently independent from Mr Trump, who has criticised judges for ruling against his bid to restrict travel from Muslim-majority countries.
Another line of attack previewed by Democratic leader Chuck Schumer is to focus on rulings Mr Gorsuch, 49, has authored in which corporate interests won out over individual workers.
Democrats will also press Mr Gorsuch on his role as a Justice Department lawyer under Bush from 2005 to 2006, when he helped defend controversial policies enacted after the September 11, 2001 attacks, including the administration's expansive use of aggressive interrogation techniques.
Mr Gorsuch's views on social issues, including a 2006 book he wrote in which he argued against the legalisation of assisted suicide and euthanasia, will be discussed too.
Republican Senator Chuck Grassley will chair the proceedings, which could go as long as four days.
Mr Trump nominated Mr Gorsuch to replace conservative Justice Antonin Scalia, who died in February last year.
If Mr Gorsuch isapproved by the Senate, as expected, he would restore a narrow 5-4 conservative majority on the court.
For months last year, Republicans refused to consider former Democratic president Barack Obama’s pick to fill the seat. The unusual Republican tactic blocked a leftward shift on the court.
Since Judge Scalia's death, the court has been divided equally 4-4 between conservatives and liberals.
Democrats face an uphill battle to block Mr Gorsuch, who like all Supreme Court justices would serve for life if confirmed.
Republicans control 52 of the Senate's 100 seats.
Under present rules, Mr Gorsuch would need 60 votes for confirmation.
If Democrats stay unified and Mr Gorsuch cannot muster 60, Republicans could change the rules to allow confirmation by simple majority.
Senators on the Judiciary Committee, which is holding the hearing, will give opening statements today and then take turns asking questions of the nominee tomorrow.