President Joe Biden flies Sunday to Japan for the second leg of a trip intended to reinforce US leadership across Asia in the face of a rising China and dangerously unpredictable, nuclear-armed North Korea. Biden is leaving South Korea, where he joined newly elected President Yoon Suk-yeol for a series of meetings, including discussing expanded military exercises to counter Kim Jong Un’s sabre rattling.

As officials from both countries warned that Kim could raise tensions with a nuclear weapon test while Biden is in the region, the US president said the democratic allies must deepen ties. At a joint press conference with Yoon, Biden cited a global “competition between democracies and autocracies” and said the Asia-Pacific region is a key battleground.

“We talked in some length about the need for us to make this larger than just the United States, Japan, and Korea, but the entire Pacific and the South Pacific and Indo-Pacific. I think this is an opportunity,” Biden said. While China is the main US rival in that struggle, Biden illustrated the acute challenge from Russia when he signed a $40 billion aid bill late Saturday to help Ukraine fight the invasion by Moscow’s forces.