Preview of Today's "Potomac Primaries" in Va., Md. and DC: Obama Expected to Roll in All Three; McCain May Be Challenged in Va, But Not in Other Two

    The primaries continue on today with contests in Maryland, Virginia, and Washington, D.C. Anything other than huge victories for Barack Obama in all three will be a surprise, continuing his momentum and putting him into the delegate lead. On the GOP side, it would be a shock if McCain doesn't win Maryland and DC; Virginia, like most southern states this time around, appears up for grabs.