A second woman has publicly accused Charles W. Herbster, the Republican candidate for governor in Nebraska endorsed by former President Donald J. Trump, of groping her at a 2019 Republican fund-raising dinner.

Elizabeth Todsen said Mr. Herbster grabbed her at the dinner in Omaha and said details of the incident reported earlier this month by the Nebraska Examiner were correct.

“For years I have struggled with an experience I had with Charles W. Herbster,” she said in a statement issued by her lawyer. “At a political event in 2019, Herbster sexually groped me while greeting my table.”

The allegations against Mr. Herbster, a millionaire agribusiness executive who is largely self-funding his campaign, have roiled the often polite world of Nebraska politics ahead of the state’s May 10 primary. The longtime Trump ally has adopted the former president’s playbook in responding to the allegations, forcefully denying them, suing his first public accuser, a state senator, and tying her to his political rivals.

A spokeswoman for Mr. Herbster’s campaign, Emily Novotny, said Mr. Herbster “absolutely and unequivocally denies all allegations.” She said he “will be taking legal action” against Ms. Todsen.

Mr. Herbster is a bitter political rival of Gov. Pete Ricketts, a term-limited Republican who like Mr. Herbster has long been a major donor to Nebraska Republicans. Mr. Ricketts is supporting Jim Pillen, a member of the University of Nebraska Board of Regents. Limited public polling of the race shows Mr. Herbster and Mr. Pillen locked in a virtual three-way tie with Brett Lindstrom, a state senator who has attracted support from moderate Republicans and from some Democrats who have changed their party affiliation to vote in the primary.

The account from Ms. Todsen follows an accusation earlier this month from Julie Slama, a Nebraska state senator who said Mr. Herbster also grabbed her at the same event.

Ms. Todsen, 26, is a former political aide to Nebraska state legislators who now works for a fund-raising company in Washington. She did not respond to messages on Saturday and her lawyer, Tara Tesmer Paulson of Lincoln, Neb., said she would make no additional comments.

Mr. Herbster denied Ms. Slama’s account and has since aired television ads tying her to his political rivals in the governor’s race while comparing himself to Supreme Court Justices Clarence Thomas and Brett Kavanaugh, who both faced charges of improper behavior during their confirmation hearings. Mr. Herbster’s TV ad claims Ms. Slama kept in contact with him after the incident and “even invited Herbster to her destination wedding.”

Ms. Slama said on Twitter on Saturday that she was “grateful for Elizabeth’s bravery in coming forward.”

Mr. Herbster and Mr. Trump are scheduled to appear together at a rally on Sunday in Greenwood, Neb. The event was originally planned for Friday night but Mr. Trump moved it, he said, because of storms forecast for the area.

Kirsten Noyes contributed research.