Last week, an aide for Vice President JD Vance reached out to the billionaire Frank McCourt.

The topic at hand was Mr. McCourt’s $20 billion long-shot offer to buy TikTok, the Chinese-owned video app. Mr. Vance’s aide wanted details about the bid, which was one of several public overtures for the app, according to two people familiar with the process.

The inquiry was one of Mr. Vance’s earliest moves toward corralling a deal for the popular app after President Trump tapped him earlier this month to find an arrangement to save it. TikTok was recently banned in the United States under a new federal law that prohibited distribution in the country if it was not sold to a non-Chinese owner, though Mr. Trump delayed enforcement of the law until early April.

Mr. Trump’s assignment plunges Mr. Vance into a fraught geopolitical and corporate negotiation over the fate of the app, which counts some 170 million American users. It is not clear who could buy TikTok in the United States, or even whether China or ByteDance, TikTok’s owner, would allow a sale. And the Trump administration is under scrutiny for its decision to disregard the law’s Jan. 19 deadline for a sale or a ban.

Mr. Vance’s involvement ensures that he and Mr. Trump — both of whom once supported banning TikTok because of national security concerns — have some public accountability for saving it, according to analysts and people involved in negotiations for a sale. Tapping Mr. Vance could also help lend negotiations more credibility, said Peter Harrell, a former Biden White House official who worked on national security, tech and economic issues.

“What he brings to the role is everybody’s going to take his call and take him seriously,” Mr. Harrell said. “Most people, given Trump has been pretty clear he’s tapped Vance for this, will assume that Vance is speaking for the president.”