On the opposite side of the state, Rep. Bill Keating (D) is the least senior member of the delegation. But his Cape-based district stretches north to Quincy and includes very Republican territory. So, he'll need to pull in Democratic voters from either Frank or Rep. Stephen Lynch's or current neighboring districts, or Keating will face a more challenging re-election bid.
According to state Rep. Mike Moran, who is leading the Democrats' efforts in the state legislature, map drawers at this point are preparing to start from scratch.
"Right now," he said, "it's a blank slate."
Some Democrats in the state involved in the process privately hope someone in the delegation jumps to run against Brown so their district can be sliced up. The top two contenders are Reps. Michael Capuano (D) -- who ran in the special election last year -- and Stephen Lynch (D).
Even their departures could pose problems. If they both run - a distinct possibility - that leaves Boston without a congressman. A case could then be made for drawing a Boston-based district for Frank because of his seniority. Frank's district currently starts just outside the city.
But while Bostoners may like Frank's seniority, that could leave him vulnerable to a challenge from an ambitious Boston city councilor -- like, say, John Connolly or Democratic rising star and former John Kerry (D) staffer Ayanna Pressley.
"There will be many maps floating about -- from the state House, Senate, interest groups -- and all of them are likely to be very different," said Larry DiCara, a former Boston city councilor who has worked extensively on redistricting in Massachusetts in the past.
DiCara said he has no idea how final map will play out, but that history has shown that when the Bay State loses a seat a member typically agrees to vacate -- either by retiring or running for another post. Back in 1962, then Rep. Laurence Curtis (R) saw his district cut sliced up and he opted to run for the Senate.
In 1992, former Rep. Brian Donnelly (D) retired from Congress even though he was only in his 40s in large part because Massachusetts was losing a seat. Donnelly then had a seat on the Ways and Means Committee and, because of his age, could have gone on to be chairman.