Five to Face off for Senate Seat
       Democrats Rep. Paul Casey of Winchester, Rep. Patricia Jehlen of Somerville, Governor’s Councilor Michael Callahan of Medford, and former Rep. Joseph Mackey of Somerville will square off in a primary election Aug. 30 to determine who will face a Republican opponent in an election to fill the 2nd Middlesex Senate seat left vacant by the death of Sen. Charles Shannon earlier this year.
       Secretary of State William Galvin announced late Tuesday that the four Democrats and Republican William White Jr. of Somerville have garnered the necessary signatures to be placed on the ballot. The special election will be held Sept. 30.