Many GOP analysts agree that Bush will benefit if voters alienated from him gravitate to Trump, who probably faces a lower ceiling of total support, than to Walker or Rubio, who have the potential to build a broader and more potent coalition. Combining results from the past three NBC/Wall Street Journal national surveys, just 27 percent of GOP primary voters said they would consider voting for Trump, far fewer than indicated they could back Bush, Walker, or Rubio.

Trump creates even more immediate problems for second-tier candidates such as Sen. Ted Cruz of Texas, former Texas Gov. Rick Perry, Huckabee, and Santorum, who have all targeted a similar group of blue-collar and conservative voters. “It just takes the energy out of the room, and it’s going to be harder for a person not in first place to break through,” says Carney, a top Perry strategist in 2012.

Still, Walker may be the candidate with the most at risk from Trump’s ascent. Longtime New Hampshire GOP activist Tom Rath, who is unaffiliated in 2016, says that in the state’s critical primary next February, Trump “really hurts Walker, because Walker’s path to winning the nomination is to do really well in Iowa and then come in here and become the dominant ideological conservative coming out of here, and parlay those two things into a good showing in South Carolina.” But, Rath adds, “Walker only can do that if the Right doesn’t splinter.”