The SEC is investigating Elon Musk's now-famous tweet about taking Tesla private, and one reason is to see whether he set out to punish investors who were betting against his company, reports Vox. If so, he did not succeed. Though Tesla's share price rose from $350 to $387 the day of his Aug. 7 tweet, it has since fallen below the initial mark. (It was around $321 on Tuesday afternoon.) Both Vox and the Guardian estimate that short sellers have made more than $1 billion since the tweet. The latter newspaper also notes that Musk has a history of battling with short sellers, a battle that has become increasingly "vituperative and personal." For example, he approved of a taunting tweet, a pair of shorts, sent to one fund manager. (More Tesla stories.)