By Patricia Zengerle
WASHINGTON, Nov 23 (Reuters) - More prominent Republicans on Monday joined the call for President Donald Trump to end efforts to overturn his election defeat and allow President-elect Joe Biden to begin the formal transition to a new administration.
Twenty days after Election Day, most members of Trump's party still refused on Monday to refer to Biden as president-elect, or to question Trump's insistence - without evidence - that he had only lost on Nov. 3 because of fraud.
Trump's legal team has suffered a string of judicial defeats in its bid to prevent states from certifying Biden as the presidential election winner, and legal experts say the remaining cases do not give Trump a viable path to overturning the election results.
Republican Senator Rob Portman - co-chairman of Trump's campaign in Ohio who rarely breaks with party leaders - said there was no evidence of widespread election fraud and called for the transition to begin.
"It is now time to expeditiously resolve any outstanding questions and move forward," Portman wrote in a Cincinnati Enquirer opinion column on Monday.
However, Portman did not refer to Biden as "president-elect" and referred to his becoming the next president as a "likely event."
Senator Lisa Murkowski - a Republican who charts a more independent course and has acknowledged Biden's victory - late on Sunday said it was time to start the full transition process. She denounced efforts by some Trump supporters to overturn election results in some states as "not only unprecedented but inconsistent with our democratic process."
Calls for Trump to accept defeat have been stronger outside Washington, even from some of his staunchest supporters, including former New Jersey Governor Chris Christie, who called Trump's behavior "a national embarrassment" in an interview on ABC.
And more than 100 former Republican national security officials published a letter on Monday asking that party leaders denounce Trump's refusal to concede, calling it a dangerous assault on democracy and national security. (Reporting by Patricia Zengerle; Editing by Scott Malone and Cynthia Osterman)