Looks like he won the seat in a gerrymandered district. This manipulation of district boundaries takes advantage of people who vote along party lines regardless of an individual candidate's qualifications.
This point simply cannot be overstated. The absolutely deplorable level of "oversight" performed by Congress is a direct function of the degree to which they've been able to insulate themselves from the electorate. Being able to select who can and can't vote against them is one of their most effective means for doing this. Indeed, this practice explains why so many of them can hold onto their seats while continuing to act against the interests of their constituents in ways beneficial to their funders.
In short, gerrymandering, closed primaries, and private campaign finance form the Triangle of Doom. In combination, they provide the noose with which Congress is choking America to death. Abuse at the hands of the NSA (and their multi-billion dollar web of contractors) is just the latest, and perhaps the most chilling example of this phenomena.
> Now, in all fairness they do have a cragy coast, but it is very clear the districts are unconscionably gamed.
I'm not sure how it was done in the source for that news article, but gerrymandering-detection algorithms should ignore natural borders in that regard. See, for example, this paper which measures gerrymandering in terms of convexity: http://mathdl.maa.org/images/upload_library/22/Polya/Hodge20...
http://en.wikipedia.org/wiki/Dutch_Ruppersberger
Dear Maryland: Please vote intelligently at your next opportunity.