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Twitter Inc. (NYSE: TWTR) continues to bleed talent. Its chief technology officer, Adam Messinger, has resigned. So has the leader of its China operations, Kathy Chen. CEO Jack Dorsey has a small cadre of three executives around him, each essential to Twitter operations, that he cannot afford to lose.

The list of executives who left Twitter in 2016, either voluntarily or because they were forced to, includes Nathan Hubbard, who ran commerce and media, Jana Messerschmidt, who ran business development, and Adam Bain, who was chief operating officer and the head of global sales. Twitter may have been able to lose one or two of these people, but not all of them. Dorsey is running Twitter with much less than a full crew.

Which executives run the company now and cannot be replaced, at least short term?

First among them is Anthony Noto, who is both chief operating officer and chief financial officer. As Twitter attempts to find firm footing with investors, Wall Street looks primarily to Noto. He also was given much of the company that reported to Bain. This includes sales, business development, data analytics and revenue-based products. Twitter says it will get a new CFO, but how soon? Noto has a blue-chip background that includes stints as a partner at Goldman Sachs and as CFO of the NFL. Finding a new job would not be hard for him.

Leslie Berland, the chief marketing officer, was recruited from American Express last year, where she was an executive vice president. In her position, she oversaw all the Amex digital partnerships. As a recruit from a blue-chip company, she is a very high-profile hire. She is in charge of Twitter’s product, sales and consumer marketing.

Vijaya Gadde is Twitter’s general counsel, which normally would not be a high-profile job. However, Twitter has been smothered with well-publicized lawsuits. These range from accusations that management made false statements about some of the key metrics by which investors track the company, in particular its number of users, to aiding the perpetrators of the Paris terrorist attacks and being partially to blame for the mass murder shooting in an Orlando nightclub. Each of these may be a major nuisance lawsuit. By the same token, they eat up time, are followed closely by the national media and are in addition to the normal, essential duties of a public company’s top lawyer.

Dorsey is down to a very few senior lieutenants to run a company that many experts and investors do not think is a viable standalone public corporation. He has to keep what remains of his top management team intact.