Only three times in the past half-century has the Democratic next-in-line secured the nomination, and in each case, the party failed to take the White House: Hubert Humphrey in 1968, Walter Mondale in 1984 and Al Gore in 2000.

So history is actually against Mrs. Clinton on the basis of her inevitability. Democrats tend not to like veterans of the presidential race running for the highest office and don’t like to pick the obvious choice. Nor, it seems, do voters in the general election…

In the past week, riding out of the West, the Hillary spoiler has appeared on the horizon. He is Brian Schweitzer, the ex-governor of Montana. An expert on energy policy, a former rancher and soil engineer, he’s disarming and funny, and he knows how to talk in an interesting way about issues because he’s from a purple state where Democrats don’t dominate.

He’s considering the run. He’s been to Iowa. He’s a new face to many Democrats, who’ll discover that he’s as populist as Warren and as vociferously anti-war as Howard Dean ever was.