Matt Murphy State House News Service Supporters of Majority Leader Ron Mariano, whose district includes Holbrook, believe the Quincy Democrat has enough votes among House Democrats to succeed Speaker Robert DeLeo if the longtime speaker steps down in the coming weeks, sources told the News Service Thursday. The snowstorm that pounded most of Massachusetts overnight Wednesday gave DeLeo a bit of breathing room after a chaotic day at the State House Wednesday where reports about the speaker's impending departure swirled. The speaker's office said nothing publicly Thursday after denying that he had a deal to join Northeastern University, and many lawmakers called and contacted by the News Service either did not respond or declined to comment as they tried to learn themselves what was going to happen.