BOSTON (AP) — State Senate Majority Leader Stanley Rosenberg is telling Democratic colleagues he plans to enforce a "firewall" between his personal and professional life after concerns were raised about social media postings by his domestic partner.

Rosenberg, an Amherst Democrat, is expected to be formally elected by his colleagues to fill the Senate president's office in January, succeeding Therese Murray, who is retiring after leading the chamber since 2007.

The Boston Globe ( reports that Rosenberg sent a letter to 33 Democratic senators in the chamber after reports that Bryon Hefner — a one-time legislative aide — had used social media to mock Murray and boast of his own influence in Senate affairs.

Rosenberg said in the letter he had "enforced a firewall between my private life and the business of the Senate."

The newspaper said Hefner had not responded to requests for comment.

When Rosenberg takes the gavel, he will claim several firsts.

He'll be the first openly gay leader of a legislative chamber in Massachusetts and the first Jewish one as well.

He'll also be the first leader in more than four decades to hail from western Massachusetts, where residents have long complained of being shortchanged by a political establishment more beholden to the larger population centers in the east.

The 65-year-old is the longest-serving member of the upper chamber.