Massachusetts Congresswoman Niki Tsongas announced yesterday she will not run again for the seat she has held since 2007. Past election results show her seat in the Third Congressional District may be less safe for Democrats than it first appears. Though Tsongas cruised to reelection in her own recent matchups, Charlie Baker won the district by 9 points in his 2014 election, one of several Republicans to fare well there recently. With voters in Tsongas’ district showing they are open to voting Republican, her retirement adds another layer of potential intrigue to the 2018 elections here in Massachusetts.