Wisconsin Gov. Scott Walker is poised to become the 15th Republican to declare his presidential bid, with at least one more candidate expected to enter soon after. But at this point, his campaign advisers said this week that they see just two principal rivals for the GOP nomination: former Florida governor Jeb Bush and Sen. Marco Rubio (Fla.)…

Iowa is the key: Walker is leading the polls there and, as a neighboring governor, he has easy access to the state. His advisers expect him to win the Iowa caucuses early next year, and they say he can follow that with top-three finishes in New Hampshire and South Carolina. They also think he can score an early victory in Nevada’s caucuses.

Walker’s advisers doubt that anyone who doesn’t win one of the four early states will move to the heavy schedule of contests in March. They also doubt that anyone will have enough delegates to clinch the nomination by the end of March, and they anticipate that the race will drag on into May before there is a winner.