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Unlike New Jersey Gov. Chris Christie, Sen. Ted Cruz of Texas, Louisiana Gov. Bobby Jindal, Sen. Rand Paul of Kentucky and other 2016 maybes, Mr. Walker has stayed home and stayed quiet.

Managerial skill doesn’t necessarily trump public impression. The concern is that some Democrats and independents whose votes he will need next year may not cotton to the idea that he will use a second term as strategic positioning to become top dog in the American political kennel.

As for Mr. Ryan, friends say he fully grasps the implications of history and probability tables. Both show that only one sitting U.S. House member, James A. Garfield, has ever won the presidency. That was in 1880, and the Ohio legislature had elected him to the Senate when he ran for president.

Even if Mr. Walker risked running statewide and was now a sitting senator, the odds wouldn’t improve much: Only three sitting senators have been elected president: Warren G. Harding, John F. Kennedy and Mr. Obama.

It may be some consolation that, for similar reasons, the playing field also may tilt against Mr. Cruz and Mr. Paul, the two other top conservatives considered first-tier potentials for 2016.

Fellow Republicans are betting Mr. Ryan fully understands that to win the chance to govern the nation, it’s better to have governed a state than to have sponsored a bill.

What should delight Mr. Walker, meanwhile, is that in the course of the 57 presidential elections held so far, 42 governors or former governors have won their party’s nomination for president — and 25 of them made it to the Oval Office.

But that also should delight Mr. Christie, Mr. Jindal, former Florida Gov. Jeb Bush, Texas Gov. Rick Perry and others.