Does the world still need US for leadership?

This year's G20 Summit of the world's major economies was a tense and sometimes frustrating gathering, exposing the United States' isolation globally on the key issues of climate and trade.

World leaders deplored President Donald Trump for pulling out of the landmark Paris Accord, and reaffirmed their commitment to fight global warming without the US.

Washington is now left in what some are calling a "club of one".

Will the world continue to look to the US for leadership? If not, who will step into that role?