In a surprise move, Joseph E. Preston announced this week he would give up the seat he recently won in the House of Delegates and challenge freshman Sen. Rosalyn R. Dance in the16th Senate District that stretches from Richmond’s East End to the Petersburg area.

Delegate Preston’s decision comes barely two months after he replaced Sen. Dance as the representative for the 63rd House District. It also appears fueled, in part, by a dispute he and Sen. Dance have over the choice of the first African-American judge for the Petersburg Circuit Court.

Sen. Dance said she tried to work with Delegate Preston, even running some proposed choices by him, but dropped the olive branch after she found he was angling to get the judgeship for himself — an allegation Delegate Preston claims is false.

Diversity in the judiciary is an issue in Petersburg, a majority-black city that currently has only white males on the bench. The first and only African-American judge, James E. Hume, retired from the Petersburg Juvenile and Domestic Relations District Court in 2009.

According to Sen. Dance, her goal during the General Assembly was to secure an African-American judge to replace

retired Petersburg Circuit Court Judge James F. D’Alton Sr. — particularly after Delegate Preston made the lack of African-American judges an issue in his campaign.

But the 67-year-old retired nurse stopped working with Delegate Preston when she said she learned he wanted the job.

Sen. Dance said she was told that Delegate Preston was offering to drop his plans to challenge her for her new Senate seat if she would leave the judgeship vacant.

“I refused,” she said, and continued to back Dennis M. Martin, a partner in the law firm of Harrell & Chambliss.

Mr. Martin ultimately was elected to the judiciary by both the House and Senate and will make history when he takes the bench July 1.

Chesapeake Delegate Lionell Spruill Sr. confirmed Tuesday that he had relayed that offer from Delegate Preston to Sen. Dance.

“He did want to be a judge,” Delegate Spruill said.

While the legislature is barred by the state Constitution from appointing a serving delegate or senator to a judgeship during the member’s term, Delegate Spruill said Delegate Preston hoped that Gov. Terry McAuliffe would appoint him to that circuit court judgeship if the legislature left the seat vacant.

Delegate Spruill said he felt “awkward” when Delegate Preston sought his support for the judgeship. Delegate Spruill said he had no intention of backing the delegate, having introduced legislation to bar General Assembly members from judicial positions until they have been out of office for at least two years.

“That’s a lie. It’s just not true,” Delegate Preston told the Free Press on Tuesday when asked if he fought Sen. Dance’s choice because he was seeking the appointment for himself.

He dismissed Delegate Spruill’s account as that of an ally of Sen. Dance. Delegate Preston said he could never make such an offer because “you cannot be a judge if you’re a sitting delegate.”

The 58-year-old attorney said he was upset with Sen. Dance’s choice for the bench because “I didn’t have any input. The result is that the first African-American Circuit Court judge for Petersburg was elected without one Democratic vote” in the House.

Delegate Preston refused to discuss whether he had interviewed Mr. Martin during the session and signaled he could support him, as Sen. Dance said.

What is evident is that Delegate Preston sought to scuttle Mr. Martin’s appointment when his name came before the House of Delegates. The Senate already had approved him for the judgeship on a 39-0 vote.

Delegate Preston, with support from Republican Delegate Riley Ingram and other members, got the House to separate the election of Mr. Martin from that of other judges in a maneuver to prevent the vote.

When the House voted on Mr. Martin, Delegate Preston, 32 other Democrats and seven Republicans, sat out the vote. The remaining Republican delegates voted 60-0 to seat Mr. Martin on the court.

Sen. Dance defended her choice, saying Mr. Martin, who lives in Petersburg, has a superb track record as a lawyer and has been a role model and mentor to Petersburg youths as a football coach and tutor. She noted that he also has provided a home for three current and former players.

She said she backed Mr. Martin — and helped secure support from the Senate’s Republican majority — after Delegate Preston rejected a proposal of the Petersburg Bar Association. She said the bar proposed elevating veteran Petersburg General District Court Judge Ray P. Lupold III to the Circuit Court and replacing him in General District Court with Petersburg Deputy Commonwealth’s Attorney Cheryl Wilson, an African-American.

Both Sen. Dance and Delegate Preston are new to their positions, having won special elections. Sen. Dance gained her seat in November when she was elected to replace former Sen. Henry L. Marsh III; Delegate Preston won his seat in January.

In announcing his challenge to Sen. Dance, Delegate Preston stated that he is running as a “true” Democrat. He has argued that Sen. Dance too often has voted with Republicans.

Sen. Dance is entering the race with the endorsement of Gov. Terry McAuliffe and other top Democrats, including Lt. Gov. Ralph Northam and Attorney General Mark Herring.