Before Robinhood Markets came along, the retail investor complex controlled by firms like Fidelity, Wellington, Charles Schwab and E*Trade was sitting pretty. But the online trading platform run by Vlad Tenev has upended that, and like any good disruptor, made its fair share of enemies along the way. That's come in the form of mountains of lawsuits, regulatory scrutiny, and distracting Washington gadflies that promise to reshape Robinhood. The backlash may be enough to leave the disruptor vulnerable to some disruption of its own.The company co-founded by Tenev filled a need in the centuries-old trading business. Until Robinhood burst onto the scene in 2019, E*Trade and Schwab made up more than 40% of the total industry's online revenue, according to IBISWorld. But Robinhood has attracted more than 21 million monthly active users, doubling in a year.