An open seat caused by the retirement of Rick Merkt (he’s thinking about running for Governor) has created a highly competitive game of political musical chairs for Morris County Republicans — an event that could be problematic for seven-term incumbent Michael Patrick Carroll, one of the Legislature’s most conservative members and an unpaid PolitickerNJ.com columnist. Carroll faces two well-known rivals: attorney Anthony Bucco, the son of the longtime State Senator; and Freeholder Douglas Cabana. Carroll beat Cabana four years ago, but GOP primaries in Morris County are nothing if not unpredictable.