BOSTON (AP) — Former Massachusetts Senate President Stan Rosenberg announced Thursday he would end his long political career after a scathing ethics report concluded he failed to protect the Senate from his husband, who has been charged with sexual misconduct.

In a one-sentence letter delivered to the Senate, Rosenberg said his resignation would be effective at 5 p.m. Friday.

The decision came amid mounting calls, including several from his Democratic colleagues, for the Amherst Democrat to resign. He stepped down from the presidency in December when allegations first surfaced against his husband, Bryon Hefner. The couple has since separated.

In a statement, Rosenberg said he was leaving the Senate because he no longer had the authority to fully represent the interests of his constituents.

He noted that the report found no evidence that he violated any Senate rules, no evidence he was aware of any alleged sexual assaults by Hefner, nor that Hefner asserted any influence over his actions while Senate leader.

But Rosenberg acknowledged findings in the report, prepared by investigators hired by the Senate Ethics Committee, faulting him for not doing more to control Hefner's access to information and access to people who worked for or had business with the Senate.

"Although, as the report states, I was unaware of many of the events attributed to Bryon, and took steps to address those incidents that came to my attention, that does not diminish my sorrow at what reportedly transpired or my sense of responsibility for what the ethics committee concludes was a failure on my part in not doing more to protect the Senate," Rosenberg wrote.

He also conveyed his "sincere apology" to anyone who'd been affected by events detailed in the report.

Investigators concluded that Rosenberg showed "significant failure of judgment and leadership," and knew or should have known that Hefner was "disruptive, volatile and abusive," and had racially or sexually harassed Senate employees.

Rosenberg also violated Senate policy by allowing Hefner access to his Senate email and to his cellphone, which Hefner on at least two occasions used to send messages to Senate staffers while pretending to be Rosenberg, the report found.

The committee had recommended Rosenberg be barred from serving in any leadership posts or from chairing any committees through 2020, and the full Senate could have imposed further punishment.

Republican Gov. Charlie Baker, Democratic Attorney General Maura Healey and at least six Democratic senators had publicly called for Rosenberg to quit after the report was released.

"I think the report made very clear that there was damage done ... to the Senate and I think it was appropriate for him to step down and I'm glad he did," Baker told reporters Thursday.

The governor said he was especially troubled that Rosenberg appeared not to keep a promise he made to Senate colleagues in 2014 to build a "firewall" between his personal and professional life.

Baker added that he had appreciated his long working relationship with Rosenberg, dating back to the 1990s when Baker was state Secretary of Administration and Finance and Rosenberg chaired the Senate Ways and Means Committee.

The first openly gay person to lead a legislative chamber in Massachusetts, Rosenberg, 68, has served in the Senate for more than a quarter century and helped craft numerous state laws.

He also played a key role in convincing the Legislature not to overturn a 2003 ruling by the state's highest court that made Massachusetts the first U.S. state to legalize gay marriage.

Hefner, 30, pleaded not guilty at his arraignment last month on charges of sexual assault, criminal lewdness and distributing nude photos without consent. The allegations involve four men.