Those dedicated to limiting harmful posts worry about Twitter under Musk.

When Elon Musk laid out the financing for his bid to buy Twitter, he promised to put up $21 billion in cash.

Even for Mr. Musk, who is worth well north of $200 billion, that’s a lot of cash to come up with. Most of his wealth is tied up in Tesla stock, and one of the most obvious ways to raise the money would be to sell some of those shares.

Given Tesla’s enormous market capitalization and its inclusion in major stock indexes, almost everybody with a 401(k) probably owns some Tesla stock. The potential for Mr. Musk to sell some of his holdings, and spend less time on Tesla as he shifts his focus to Twitter, has raised questions about the outlook for Tesla’s share price. The stock dived 12.2 percent on Tuesday, as the S&P 500 index fell 2.8 percent.

Tesla’s shares have lost about 20 percent of their value since Mr. Musk first revealed that he had bought a big stake in Twitter, kicking off takeover speculation. Jim Cramer, the frenetic host of CNBC’s “Mad Money,” accused Tesla of “hurting this market pretty badly.”

Has Musk sold off stock to fund his Twitter bid?

It’s too early to know. Such sales would have to be reported to the Securities and Exchange Commission, but those reports are not instantaneous. Sales can take a few days to be made public.

What impact would sales by Musk have on Tesla’s share price?

Even a sale of a huge portion of Mr. Musk’s Tesla stock would be unlikely to affect Tesla’s share price for too long.

Mr. Musk is Tesla’s biggest shareholder, holding about 17 percent of the company’s shares — about 175 million shares in total.

He would need to sell nearly 24 million shares at Tuesday’s price to generate $21 billion in cash. That’s about an average day’s trading volume for Tesla stock — a lot, but not enough to overwhelm the market. On Tuesday, about 45 million shares were bought and sold.

Mr. Musk’s financing package for Twitter also includes $12.5 billion in loans using his Tesla shares as collateral. If Tesla’s stock falls far enough, lenders would require Mr. Musk to add collateral to support the loans, potentially forcing him to sell more stock to come up with the cash.

Mr. Musk has sold off large tranches of Tesla’s stock before. Last year, he sold some 15 million shares, worth more than $16 billion, over two months. Those sales did not appear to measurably drive Tesla’s price down, though it’s unknowable whether the price would have gone up had he not been selling.

When Tesla’s stock drops, what happens to the rest of the market?

Tesla is a component in both the S&P 500 and the Nasdaq composite index. In addition to being barometers of how stocks in the United States are performing, both indexes are mirrored by numerous mutual funds that are invested in widely.

The S&P 500, considered the benchmark U.S. index, weights companies according to their market value. Tesla, which is worth about $900 billion, is one of the most influential stocks in the index.

For every dollar that Tesla’s stock dropped on Tuesday, the S&P 500 lost 0.099 points, according to Howard Silverblatt, a senior index analyst at S&P Dow Jones Indices. That means the drop in Tesla’s stock accounted for nearly a tenth of the S&P 500’s fall on Tuesday.

“So it did have a very large impact,” Mr. Silverblatt said, but “not the highest.” Apple, with nearly three times the valuation of Tesla, has far more impact. Its stock’s drop of 3.7 percent on Tuesday contributed more to the overall index’s decline.

So why did Tesla’s stock fall?

Tesla is a famously volatile stock. Tuesday’s 12.2 percent fall was its worst daily decline since Sept. 8, 2020, when it shed about 21 percent of its value. But in the past six months, Tesla shares have twice fallen nearly 12 percent, on Nov. 9 and Jan. 27.

Some — including Mr. Musk, at times — have suggested that Tesla is overvalued. Among those who believe in Tesla’s valuation, which is much higher than rival automakers’ relative to the size of its operations, a lot of the argument depends on Mr. Musk’s stewardship. Even Tesla acknowledges this, stating as a risk in its most recent quarterly report: “We are highly dependent on the services of Elon Musk, techno-king of Tesla and our chief executive officer. Although Mr. Musk spends significant time with Tesla and is highly active in our management, he does not devote his full time and attention to Tesla.”

A lot about Mr. Musk’s plan to buy Twitter is unknown, including how involved he would be. “Tesla investors are worried that Musk might spend too much time trying to fix the social media giant’s problems and that will take away his laserlike focus” on Tesla, said Edward Moya, a senior market analyst at OANDA.

Or as Mr. Silverblatt put it: “It’s anticipation of something that hasn’t occurred yet. It will be a while before we know anything.”