Taiwan on the line: Trump phone call alarms China (part 2)

A congratulatory phone call. Why not answer? What's the worst that can happen? Donald Trump answered the call from Taiwan's nationalist president, a first since Washington switched diplomatic allegiances from Taipei to Beijing in 1979. Official media on the mainland called it "rookie diplomacy" but that might be giving The Donald the benefit of the doubt. What US policy now for the region? How will Beijing react?