The map would have the secondary effect of shoring up Harris, who narrowly lost his first race in 2008 before beating then-Rep. Frank Kratovil (D-Md.) in a 2010 rematch.

Bartlett's new district wouldn't be a slam-dunk for Democrats if he ran — he has an unorthodox voting record, including support of some Democratic positions on renewable energy and civil liberties, and the new district leans Democratic, but not overhwelmingly so. But the 85-year-old might choose against running in his first tough race in decades.

Democrats had pondered targeting both Republicans, but that would have forced a complete rejiggering of the current map and could have put some of their own incumbents at risk.

Republicans get to draw many more districts after landslide wins in 2010 gave them control of statehouses and governors' mansions across the country. This has allowed them to target Democrats in states including North Carolina and Georgia. Maryland was one of only a few states where Democrats got to draw the lines unimpeded.

The map, proposed by Democratic Gov. Martin O'Malley, will likely face little resistance in the Democratic-controlled statehouse.