Massachusetts Gov. Deval Patrick (D) signed the state’s new Congressional lines into law today. The new map reduces the number of districts in the Bay State from 10 to nine and mostly protects incumbents.

The late October retirement announcement from Rep. John Olver (D-Mass.) eased the task of the Democratic-controlled state Legislature, which was faced with drawing at least two Members of the all-Democratic delegation into the same district.

Under the new map, there is a district for each Member, although freshman Rep. Bill Keating (D) will have to move his primary residence.

The new map did little to shore up the delegation’s most vulnerable Member, Rep. John Tierney (D), whose wife pleaded guilty to federal tax charges last year. He is likely to face former state Sen. Richard Tisei (R), who was the GOP nominee for lieutenant governor in 2010. Republicans in Boston and Washington, D.C., consider Tisei the party’s best hope of picking up a seat in the Bay State.

Still, the heavy Democratic tilt of the state will make Tisei’s climb tough. The last Republican Congressmen to represent Massachusetts, Reps. Peter Torkildsen and Peter Blute, lost in 1996.