In opening statements before a hearing committee of the D.C. Board on Professional Responsibility, the city's top disciplinary counsel said Giuliani breached attorney ethics rules in a November 2020 lawsuit on behalf of the Trump campaign in Pennsylvania.

The lawsuit, which sought to throw out votes cast in the state, was rejected by a judge. A federal appeals court refused to let the campaign file a revised complaint.

Hamilton "Phil" Fox of the D.C. Office of Disciplinary Counsel told Monday's panel that the former the New York City mayor, once the top U.S. prosecutor in Manhattan, "weaponized his law license to bring a frivolous action in an attempt to undermine the Constitution."

Giuliani's lawyer, John Leventhal, said his client should not face charges because the judge did not accept and never considered the only version of the complaint in the Pennsylvania lawsuit that Giuliani himself signed.

Leventhal also faulted the judge's reasons for dismissing the Pennsylvania lawsuit and noted that the court did not sanction Giuliani over his arguments.

Giuliani was the first witness called on Monday. He described how he began leading the Trump campaign's legal efforts to challenge the 2020 election results, including his work on the Pennsylvania lawsuit.

The hearing committee will recommend whether Giuliani should be penalized after hearing evidence from both sides this week.

Any discipline, including suspension of Giuliani's law license or disbarment, must be imposed by a D.C. court.

Giuliani's New York law license was suspended in June 2021 after a state appeals court found that he made "demonstrably false and misleading" statements that widespread voter fraud undermined the election.

His D.C. law license was temporarily suspended after the New York decision.

(Reporting by Jacqueline Thomsen in Washington; Editing by David Bario and Bill Berkrot)

By Jacqueline Thomsen