RICHMOND, Va. (AP) – One of Virginia’s most powerful politicians is stepping down.Republican House Speaker William J. Howell said yesterday he is retiring and will not seek re-election when his term ends in January.House Majority Leader Kirk Cox is expected to be Howell’s successor, though other Republicans may try to challenge him.Elected as speaker in 2003, Howell helped grow a near GOP supermajority in the House thanks in part to the favorable legislative boundaries drawn during the last redistricting.The 73-year-old has promoted conservative, business-friendly policies while helping thwart parts of three Democratic governors’ agendas, including Gov. Terry McAuliffe’s push to expand Medicaid.The quick-witted speaker has not been ideologically inflexible. He helped former GOP Gov. Bob McDonnell pass tax increases to pay for a transportation-funding overhaul.