Maryland is increasingly a city-state -- many of its districts are at least partially in either metropolitan Washington, D.C., or Baltimore. The state has long been a Democratic stronghold. In the 19th and early 20th centuries, a Democratic machine in Baltimore combined with voters on the culturally southern Eastern Shore to form a Democratic majority. In the later 20th century, the Democrats lost the Eastern Shore but found increasingly receptive voters in the suburbs of D.C.
Oddly enough, in the early 1970s, Maryland had two Republican senators. One, Charles McC. Mathias, was cut from classic New England establishment Republican cloth. As a result, even in a terrible GOP year such as 1974, he was able to win with a convincing 17-point margin of victory. The other, J. Glenn Beall Jr., was conservative and in 1976 suffered one of the 10 worst drubbings of any Senate incumbent in history (his father had a top-five loss in 1964) at the hands of Democrat Paul Sarbanes.
Sarbanes retired in 2006, and Republicans were initially bullish on the prospects of then-Lt. Gov. Michael Steele. But Steele faded down the stretch and lost to Rep. Ben Cardin. Cardin has compiled a solidly liberal voting record in the Senate over the course of a generally low-key term. He hasn't exactly set the world on fire, but the Republican nominee, ex-Secret Service agent Daniel Bongino, hasn't shown much evidence that he can make this a competitive race.