Any examination of a statewide race must start with voter registration counts. Here are the voter registrations by county as of 10/31/09.

Overall, the Democrats have an absolute majority (at 56.9%) and outnumber Republicans by better than two-to-one. But the total numbers mask the geographic domination of the Democrats and the regional isolation of the GOP.
The Democrats have more than 50% of registered voters in eight jurisdictions: Baltimore City and Baltimore, Charles, Dorchester, Kent, Montgomery, Prince George’s and Somerset Counties. Those jurisdictions account for 60% of the state’s registered voters. The Republicans have more than 50% of registered voters in two jurisdictions: Carroll and Garrett Counties, which account for just 4% of the state’s registered voters.
Let’s lower the threshold to 40%. The Democrats have more than 40% of registered voters in 18 jurisdictions (all except Allegany, Carroll, Frederick, Garrett, Queen Anne’s and Washington Counties) that account for 88% of the state’s registered voters. The Republicans have more than 40% of registered voters in eight jurisdictions: Allegany, Carroll, Frederick, Garrett, Harford, Queen Anne’s, Talbot and Washington Counties, which account for just 17% of the state’s registered voters.

Registration does not always determine voting behavior. Maryland is a state in which Democrats can and do vote for Republicans, the most successful of whom has unquestionably been Bob Ehrlich. But all of the above means that the Democrats have a far broader reach across the state than does the GOP. Western Maryland is the only region in which the Democrats struggle to compete. The Republicans are non-competitive in three of the state’s four biggest jurisdictions (Baltimore City and Montgomery and Prince George’s Counties) and lag Democrats in Anne Arundel and Howard Counties, fast-growing Charles County and even some parts of the Eastern Shore. All of this is a hurdle that any statewide GOP candidate would have to overcome.
We’ll look at historic registrations and turnout in Part Two.