Like a clipper ship at full sail, Hillary Clinton is sweeping toward the Democratic nomination. She has delegates in the hold, party elites at her back, and she clearly wants to tack toward the middle where general elections are won. But Bernie Sanders keeps forcing her to the left. The senator from Vermont, while still losing, is wildly outperforming expectations. She’s won 23 states, but he’s taken 19 — pirating many of the party’s young voters in the process. And liberals love him.

This is no small matter. Over the past 15 years, a study by Pew has found that Dems who call themselves conservative or moderate have been retreating, while self-described liberals have been rising. They are now the biggest faction in the party, and many have been disappointed by the lukewarm liberalism of the Obama White House.

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They can hardly contain their glee when Sanders raises his fist and shakes his gray mane in righteous fury. Down with the rich! Up with working folks! Free college for all! Prepare yourself, Washington, you’re about to be boarded!

So Clinton has been working the tiller, trying to steal his wind. She started off talking about pushing the minimum wage up to $12 an hour. He said $15. Now she’s right there with him.

He came into the race railing about the Keystone XL pipeline. After many long months of noncommittal statements, soon enough, she turned that way too.

He’s wanted a single-payer health insurance plan from the government for a long time, and just this week she took a big step in his direction.

Trade deals? He’s a skeptic. She loves them — oh wait, look who is a skeptic now too.

Like it or not, this is a smart strategy aimed at making sure all those mutineers against the party bosses settle down, give up on Sanders and fall in line. Because she knows when the true buccaneer of politics these days, Donald Trump, sails into the bay with his cutlass slashing the autumn air, she may need all hands on deck.

(CNN’s Tom Foreman is the author of "My Year of Running Dangerously")