Commonwealth Magazine, via email.
Dempsey’s decision to leave the House indicates he was tired of waiting around for DeLeo to retire so he could move up. Several sources said they believe DeLeo, who pushed through the elimination of an eight-year term limit on the speaker’s position in January 2015, is likely to remain at the chamber’s helm for another three to four years. “Brian just wasn’t willing to wait around that long,” said one source.
The House is run in a top-down fashion by DeLeo, who himself moved up from the Ways and Means job to the speaker’s position in 2009. Dempsey meshed well with DeLeo; both lean conservative for Democrats and generally oppose new taxes. Dempsey entered the House in 1991, the same year as DeLeo, and the two officials are close friends who enjoy broad support within the body.
Sparing you my usual screed about how I hate when politicians step down early (Didn’t they pledge to serve?), I’ll just note that this change in the line of succession may prompt some action down below.