Then came war. On Tuesday, Citron Research founder Andrew Left, an activist investor and short seller, tweeted that he’d share five reasons why GameStop’s stock would plummet to $20 fast in an upcoming livestream. (The stock had by then climbed to $41.) “We understand short interest better than you and will explain,” he wrote. In a YouTube video, Left argued that GameStop is “a failing, mall-based retailer,” and that its value is “not based on any fundamentals, [which] just shows the natural state of the market right now.”On Friday, Left set up a second Citron Research Twitter handle, claiming …