The combination of Mr. Walker’s advantage in Iowa, his broad acceptability and his fund-raising potential gives him perhaps the clearest path to the nomination of any Republican candidate. Unlike recent winners of Iowa, like Rick Santorum and Mike Huckabee, who were unacceptable in the blue states and lacked the resources to win the nomination, Mr. Walker could plausibly follow up an Iowa victory with a win in New Hampshire, especially given the divided nature of this year’s field.

No other Republican combines a natural factional base in an early primary state with the potential for broad acceptability throughout the party. Jeb Bush will face persistent resistance from the party’s conservative wing, even if his combination of superior resources and just enough appeal could allow him to prevail in a protracted fight. The many conservatives competing with Mr. Walker in Iowa, like Ted Cruz or Mr. Huckabee, have won loyal but narrow support by embracing messages that alienate much of the party. Marco Rubio, perhaps the only candidate who appeals more broadly throughout the party than Mr. Walker, does not have a natural base of support in the party and has struggled to break through.

But a straightforward path to victory is no guarantee of victory. In August 2011, if you had asked “who is in the best position to win the Republican nomination?” many might have responded “Rick Perry.” On paper, he was broadly acceptable throughout the party and to its establishment, he had a strong pitch to conservative voters desperate for an alternative to Mitt Romney, and he led polls in Iowa and nationally in 2011. But he promptly blew his opportunity with a series of missteps that made him seem woefully unprepared for the presidency.