BOSTON — The state Senate elected an acting president after former President Stan Rosenberg changed course Monday and agreed to relinquish his leadership responsibilities amid sexual misconduct allegations involving his husband.

Rosenberg, a Democrat, originally had said he would recuse himself only from any matters related to the investigation of the allegations against his husband, Bryon Hefner.

Rosenberg informed senators just prior to a closed-door Democratic caucus that he would step aside temporarily, though he would remain in the Senate.

"I believe taking a leave of absence from the Senate Presidency during the investigation is in the best interest of the Senate," Rosenberg said in a statement. "I want to ensure that the investigation is fully independent and credible, and that anyone who wishes to come forward will feel confident that there will be no retaliation."

Following the nearly eight-hour Democratic caucus, the Senate voted to elect Democratic Majority Leader Harriette Chandler as acting Senate president.

Chandler will continue in the post through the course of an investigation into Rosenberg and his staff. Chandler said she is not interested in serving in the post after the investigation.

"I don't have to tell you how turbulent and tragic and surprising and very sad the last four days have been for all of us," Chandler said. "What's most important right now is that we move toward a swift and resolute conclusion to this whole sad event."

Chandler said the Senate admires the courage of those who came forward to tell their stories.

"No one who serves, works or does business in the Massachusetts Statehouse should feel unsafe, coerced or unsupported," she added.

Rosenberg, who has not been accused of wrongdoing, expressed shock over the allegations reported last week by The Boston Globe. He maintained that his husband had no influence over his policy decisions or actions by the Senate.

Several men told the Globe that Hefner sexually assaulted or harassed them, including three men who said Hefner grabbed their genitals. The men, who were not named by the Globe, said they did not report the abuse partly because they did not want to alienate the powerful Senate leader.

Attorney General Maura Healey and Suffolk County District Attorney Daniel Conley, both Democrats, said Monday they were prepared to launch an investigation and said anyone with information should feel free to contact either of their offices.

The two said they are committed to providing every survivor of sexual assault "a safe, respectful, victim-centered environment."

Lawmakers also voted Monday to refer the case to the Senate Ethics Committee and authorize the committee to hire a special investigator to conduct an independent probe. The investigator would be given the authority to summon witnesses and have access to Rosenberg's office.

Chandler said lawmakers will review the Senate's sexual harassment policy and create an independent reporting entity for those who have been harassed.

The investigation will focus on whether Rosenberg knew about Hefner's behavior or if Hefner had any clout when it came to matters before the chamber. Rosenberg said Friday that Hefner would soon enter treatment for alcohol dependency.

Republican Gov. Charlie Baker, through a spokeswoman, called Rosenberg's decision to step down "the right one." Baker supports the decision of Healey and Conley to open the possibility of a criminal investigation.

Democratic U.S. Sen. Elizabeth Warren weighed in Monday, telling reporters "the charges against the Senate president's husband are disgusting and the people who have leveled these charges have a right to be heard and to be respected and protected."

The scenario that unfolded on Monday was without modern precedent in the Massachusetts Senate.