New Delhi, June 13 -- Greg Moriarty spent nine years running Australia's Defence Department before he became the country's voice in Washington. His first task in the new posting is a delicate one: to convince Australians that the United States, under a president who has spent the year reordering America's alliances, still stands behind the most expensive defence undertaking in their nation's history.

the submarine pact, and the tariffs that still sit between the two economies.

The reassurance matters because the doubt is no longer confined to the usual quarters. AUKUS now carries an estimated price of 368 billion Australian dollars, and the version Canberra is buying has narrowed since the pact was signed. The plan is now built around t...