Senator James Paterson said while he was still a strong believer in the AUKUS alliance, through which Canberra will acquire nuclear-powered submarines from Washington, he was also a realist as the Trump administration had changed the status quo.
"It is unlike any administration which has preceded it, and because it is the Trump administration mark two, it can't just be dismissed as an aberration of history at a moment of a single presidency," he told an ANU national security conference on Wednesday.
"Particularly when it looks like that the successors to Trumpism, the inheritors of Trumpism - whether it's JD Vance or someone else - are just as fervent believers in the Trump doctrine when it comes to foreign policy and national security as he is.
"So Australia has to adjust to the reality of that world, it's no longer adequate to just hope that the United States will come to our aid in a time of crisis."
Australia needed to be both a better ally to the US and make a bigger contribution to the alliance by investing further in its own defence capability, Senator Paterson said.
"We also have to prepare for a world where we may have to look after ourselves and fend for ourselves in a region where we are not the predominant power," he said.
This meant improving asymmetric capability - where a smaller, middle power like Australia would pack a punch above its weight to deter larger adversaries from attacking.
"That does look like more missiles and drones and other capabilities like that," he said, pointing to Ukraine sinking Russia's Black Sea fleet with cheap drones.
Opposition industry spokesman and former special forces soldier Andrew Hastie pointed to Iran choking the major oil route through the Strait of Hormuz as an example of Australia's vulnerability to global events.
The nation needed to ensure it had the industrial capacity and fuel supplies to be self reliant as it couldn't rely on an international world order, Mr Hastie said.
"The post-Cold War global order is now dead, and buried alongside it in the cemetery is the peace dividend that underwrote our trade and prosperity," he told the conference.
Australia had failed to anticipate the rise of China, Iran and Russia, and their interest in undermining peace underwritten by US hard power, Mr Hastie said.
The failure to increase military capacity to prepare for global uncertainty meant it couldn't help in major events, such as sending a warship to the Strait of Hormuz to aid in freedom of navigation as Iran blocks oil tankers, he said.
"That's because our frigates aren't protected against Iranian drones and missiles; it's a sad state of affairs," he said.
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