While Australia's elevation in the alliance will no doubt have real benefits, the circumstances of its recent rise - and the unpredictability of its architect - should provoke some wariness as well.

The US-Australian alliance is a long and storied one, as deserving of the term "special relationship" as the US-UK alliance. From a century of fighting side by side in foreign wars to close economic and cultural ties, the ties between the two countries have seldom been in any real danger of severing.

Until the arrival of President Trump.

Australia, by virtue of being a long-term ally, a democracy, and friendly to President Obama, already had three strikes against it on Trump's first day in office. When the new president started shredding alliances left and right, Australia was not spared. Within a week of taking office, Trump and Prime Minister Malcolm Turnbull had a heated phone call over refugees. At the time, the New York Times worried that the argument "threatened to do lasting damage" to bilateral relations.

That did not happen: a year later, the rift had healed. When Turnbull visited the White House in February 2018, the Washington Post referred to him as "one of the US president's closest partners."

But that closeness was as much about the failure of other alliances as it was about the success of the US-Australian partnership. In the intervening year, US relations with its European and Canadian allies had frayed. True, the White House was making plans for a state visit from French President Emmanuel Macron (the first and only such dinner before Morrison's), but whatever affection bound Macron and Trump together during that visit had evaporated within just a few months.

These crumbling alliances helped bring the US and Australia closer, but they also underscored how fundamentally the nature of alliances with the US had changed in a very short period of time. The Western alliances of the 20th century had been premised on a shared set of values, centred on democratic governance. Members of these alliances didn't always do a great job of living up to those values, but they maintained a rhetorical and increasingly real commitment to them.

Morrison knows these values well - he spelled them out in his opening speech, in which he praised America's "moral purpose": "We believe in the capacity of enterprise and free markets to create wealth and to lift all, and for free and fair trade to bring nations closer together. We believe that governments derive their power from the consent of the governed and that the ballot box and democracy is the surest foundation for peace and security. And we believe in the rule of law and freedom of association."

Such words would have read as boiler-plate diplomatic language just a few years ago. Now, they raise suspicions that the prime minister was trolling the tariff-loving, law-skirting democracy sceptic who currently occupies the White House.

The alliance may still be value-based - a number of commentators have stressed the similarities between Morrison and Trump, as they did the similarities between Turnbull and Trump - but the values are not those that once bound the US and its Western allies together.

Those similarities are likely part of the reason Trump has kept Australian leaders close. Another is the mounting tensions between the US and China. That those tensions have been more economic than military is little comfort for Australia, which is reliant on trade with both countries to keep its economy strong. While its strong ties to the US and China elevates Australia's importance in this new quasi-cold war, it also puts Australia at risk of being pinched by their escalating trade war.

Some nations benefit from conflict between great powers, but Australia has no guarantee it will be one of those, especially if greater tensions means greater pressure to choose between China and the United States.

The other worry that should trouble the Prime Minister's sleep tonight is the unpredictability of his host. Yes, the alliance looks to be in good shape, and an evening spent gobbling down apple pie in the Rose Garden will certainly bolster that feeling. But Donald Trump has a history of reversing course, often abruptly and with little provocation. No deal is ever truly sealed: whether he fails to follow through or does a quick about-face, Trump is governed by whim. Allies who rely on his word will soon learn how little it's worth.

That doesn't mean that Australia should not press its advantage in this moment. Trump is shockingly vulnerable to flattery, and Morrison is eager to offer it up. But Australians should bear in mind that this new closeness to the Trump administration comes at a cost, and that the state dinner may end up having a much higher price tag for Australia than for the US.