Worst of all, from Warren’s point of view, would be the policy ambition of a Hillary Clinton presidency. The big ideas exciting the Democratic center are free community-college education (advanced by President Bill Clinton back in the 1990s, now endorsed by President Barack Obama) and some kind of national pre-kindergarten program. Both initiatives are premised on the assumption that wage stagnation is traceable to educational deficiencies. These initiatives would be very expensive, but ultimately they are not very radical: They seek to improve the American worker, not to reform the American job market.

What if you agree with the Democratic left that the problem is not the employee, but the employer? What if you think that Thomas Piketty is right, that capital is overpaid, that the wealthy have gained too much political power and are using that power to enrich themselves further? You’re not likely to get much from a Clinton presidential campaign, still less from a Clinton presidency.

Only one thing could change this dreary calculus: a credible challenge from Hillary Clinton’s left. Such a challenge would force Clinton to shift left—and might extract commitments that would bind a future Clinton presidency, as the right extracted commitments from Mitt Romney in 2012. Even better, from the left-wing point of view: A left-wing challenger might actually win.

Just why, after all, is Hillary Clinton so inevitable? What does Clinton bring to this contest that she didn’t bring to the contest she lost in 2008? Have her ideas become more exciting? Her speeches more inspiring? Her story more relatable? The only difference this time is that there’s no alternative candidate competing against her. And that difference could change with one word from Warren.

Could Warren do it? Of course she could. More than almost anybody running in 2016—more even than Republican insurgents like Ted Cruz and Rand Paul—Warren has both her message and her constituency ready to hand. Hillary Clinton speaks to those Democrats who feel that Barack Obama went too far. Elizabeth Warren speaks to those Democrats who feel he didn’t go far enough. And if Warren’s supporters aren’t as spectacularly wealthy as Clinton’s, together—as Barack Obama proved in 2008—they can give more than enough to fund a winning campaign.

What about the general election? Not since 1960 has the Democratic party won the presidency with a Massachusetts liberal, and even that victory proved a squeaker. But elections are comparisons, and if Warren has weaknesses in such a contest, Hillary Clinton has more. Suppose the Republicans nominate Jeb Bush, as seems at least plausible. What’s the Clinton message in such a contest? “My husband had a better job creation record than your brother”? She won’t be able to portray him as a candidate who owes everything to his famous last name. She won’t be able to ask questions about how he made so much money so fast without delivering any real world good or service to anybody. She won’t be able to dismiss him as out-of-touch with the realities of everyday life. She can’t say that he’s a throwback to the politics of 20 years ago. Each and every one of those most promising lines of attack on Jeb Bush will be foreclosed to Hillary Clinton, because every one of them will be even more damaging to her than to him. But Elizabeth Warren can speak to them. There’s no national Democrat who can draw a sharper contrast with Jeb Bush than Warren; no Democrat who has more in common with him than Hillary Clinton.