“It’s not about Republicans and Democrats,” said Newt Gingrich, the former Republican House speaker and an ally of Mr. Trump. “It’s lots and lots of normal, everyday people who began to figure out they really got ripped off for the last year just like they got ripped off in 2008 and 2009.” He added, “What you’re seeing is an almost spontaneous cultural reaction in which the little guys and gals are getting together and going after the bigs, so the bigs are having to rig the game in order to survive.”

The reality is more complicated. There’s little sign of any central political mission shared by the millions of amateur traders who combined to squeeze at least two hedge funds that bet against the stocks of companies like GameStop and the movie chain AMC. One of the originators of the scheme is far from a “little guy,” with the financial resources to allegedly transform an initial investment of $53,000 into $48 million. Over all, only about half the country owns any stock at all.

On Reddit, the online site that helped fuel the surge, few of the mostly young participants frame their flood of investments in clearly partisan terms. Yet many write of being driven by anger over the 2008 financial bailouts that kept the big banks afloat while 10 million Americans lost their homes.