He “punted” on a question about evolution in London; he did not distance himself from Rudy Giuliani, the former New York City mayor, after Mr. Giuliani questioned whether President Obama loved America; he said he didn’t know whether Mr. Obama was a Christian; and on Thursday, at a conservative conference, Mr. Walker argued that his experience facing down union protesters in Madison prepared him to defeat the Islamic State, the terrorist group. He later acknowledged, “There’s no comparison between the two.”

My review of Mr. Walker’s television advertisements; debates; newspaper and television interviews; and speeches shows that he can be a candidate who deftly deflects and reframes tough questions. On that basis, it seems right to assume that Mr. Walker is less prone to an implosion than past Republicans who have surged in the polls, like Rick Perry, the former Texas governor. As I’ve mulled his chances over the last few years, my main question has been whether Mr. Walker would break out, not whether he could sustain momentum.

Image Protesters in Madison, Wis., in 2011, the year of a showdown between Gov. Scott Walker and unions in the state. Credit... Nicole Bengiveno/The New York Times

I asked Charles Franklin, a professor at Marquette University Law School in Wisconsin and director of the Marquette Law School poll, what his experience watching Mr. Walker over the last four years suggested about his mettle as a presidential candidate. He said Mr. Walker was “capable” and “very tactical,” someone who “thrives with a Democratic opponent and can do as well with Republicans.” His electoral record is certainly consistent with that view.

Nonetheless, most Republican elites are less familiar with Mr. Walker than they are with Jeb Bush or the candidates from the Senate or near New York City who have captured more media attention over the last few years. For most people, Mr. Walker’s audition is starting now, and, whether conservatives think it’s fair or not, his performance has raised doubts.