AUSTIN, Tex., March 29 — In 1999, Matthew Dowd became a symbol of George W. Bush’s early success at positioning himself as a Republican with Democratic appeal. A top strategist for the Texas Democrats who was disappointed by the Bill Clinton years, Mr. Dowd was impressed by the pledge of Mr. Bush, then governor of Texas, to bring a spirit of cooperation to Washington. He switched parties, joined Mr. Bush’s political brain trust and dedicated the next six years to getting him to the Oval Office and keeping him there. In 2004, he was appointed the president’s chief campaign strategist....