Donald Trump was on a flight back from Florida in late July when he announced the US faced a new threat that needed to be banned: TikTok, the Chinese-owned video app which has become hugely popular among younger Americans.

Delivered to reporters on Air Force One, the president’s decision came as a complete surprise to the lawyers and White House aides who had been working to finalise a deal that would place TikTok’s US business in the hands of Microsoft, the Seattle-based tech giant. “We are not an M&A country,” Mr Trump said, using a term for mergers and acquisitions.

The presidential intervention set off a frenetic two months of wrangling, intrigue and lobbying that has marked the most politicised takeover battle in recent American history — and one that has still not been concluded.