A woman has been arrested in Los Angeles for allegedly spying on Taiwan President Lai Ching-te's son for Beijing — bad news for US-China relations and for anyone hoping the two sides are heading toward calmer ties.

• The FBI arrested a 34-year-old Chinese woman at Los Angeles airport as she tried to fly to China; she is accused of watching Lai's son and his family on Beijing's orders.
• Lai's son appears to live in the US and work in Washington state, and the suspected goal was dirt that could be used to pressure or embarrass Taiwan's president.
• Former Vice President Mike Pence called China the biggest economic and strategic threat the US faces this century.
• The FBI says the case shows China running operations on American soil, part of a wider pattern that includes trying to get inside the US military, companies, and universities.
• The striking part is that Beijing apparently believed it could do this inside the US without consequences.

Outlook: Expect the case to harden Washington's skepticism of talk about "strategic stability" with Beijing and to fuel more spy prosecutions.