Perhaps a more difficult issue to proving a violation of Rule 10b-5 would be showing that the defendant acted with an intent to defraud, or at least was reckless in making statements that were misleading or incomplete. Mr. Musk gave an emotional interview to The New York Times about how “excruciating” the past year has been. Unfortunately, the securities laws do not provide an exhaustion defense, and just saying “never mind” does not necessarily dissipate the market impact of statements.

Another danger to Tesla and Mr. Musk is this: The S.E.C. could seek to bar Mr. Musk from serving as a director or an officer of a public company if he is found to have committed fraud. Such a ban would cause Tesla significant problems. It could force Mr. Musk out of Tesla. And if the company was taken private, an order barring him from a leadership role at a public company would complicate Tesla’s return to the public markets.

One possible defense to a potential fraud charge would be that Mr. Musk reasonably believed there was sufficient financing at the time he posted the statement.

But there are hurdles to that defense. The S.E.C. would need to prove only that Mr. Musk’s actions had been reckless, defined as a significant departure from the proper standards of business conduct. Evidence that Saudi Arabia’s sovereign wealth fund or the private equity firm Silver Lake had reservations about financing a deal, or that the discussions were still continuing, may be enough to show recklessness.

The S.E.C. may investigate whether Mr. Musk sought to drive up the price of Tesla’s shares to harm short-sellers, a group he has blamed for much of his stress over the past year. Issuing a statement designed to affect the share price can constitute market manipulation in violation of Rule 10b-5.

It is a difficult violation to prove. It requires the S.E.C. to show that the person acted with that specific purpose. Making a case based only on a single tweet would be a challenge even though the statement drove up Tesla’s stock. Mr. Musk could offer a more innocent explanation, such as he was merely jumping the gun to reveal his desire to take the company private.