Democrats don’t need any more presidential candidates. They need senators.

At least on paper, Sen. Sherrod Brown (D-OH) looks like a powerful contender for the presidency. He has a quarter-century of experience in Congress. He brings a left populist appeal without the baggage of being a self-described “socialist.” And he’s a winner. Brown won reelection by nearly seven points last November, despite Ohio’s Trumpian tilt and despite the fact that Republicans swept the state’s other major statewide offices.

Nevertheless, Brown an...