Senator Elizabeth Warren, furious about President-elect Donald J. Trump’s appointments of finance industry insiders, took to Facebook a little over a week ago to fire off a message to her nearly 2.5 million followers.

She took aim at an individual she described as a “hedge fund billionaire” who is “thrilled by Donald Trump’s economic team of Wall Street insiders.”

The hedge fund manager she condemned was Whitney Tilson, who runs Kase Capital. Ms. Warren — the fiery Massachusetts Democrat who is known for her stern mistrust of Wall Street — called him out by saying, “Tilson knows that, despite all the stunts and rhetoric, Donald Trump isn’t going to change the economic system.” Then she added, “The next four years are going to be a bonanza for the Whitney Tilsons of the world.”

There’s one rather glaring problem with Ms. Warren’s attack: Mr. Tilson happens to be one of the few financial executives who publicly fought Mr. Trump’s election and supported Hillary Clinton. A lifelong Democrat who was involved in helping to start Teach for America, Mr. Tilson also happened to be one of the rare Wall Street executives who had donated to Ms. Warren and actively sought new regulations for the industry. Recently, he gave Mrs. Clinton $1,000 so he could see Ms. Warren speak at a campaign fund-raiser. (He’s also far, far from a billionaire.)