The US vows to get tough with the world's bad guys - but can they afford to?

Washington's budget gridlock could affect Australia if the United States' military leadership starts to "atrophy", including in the Asia region because the Pentagon cannot get the money it needs, a new think-tank report has warned.

Despite US President Donald Trump's sustained tough rhetoric about the various security challenges facing the world, such as North Korea, the new analysis states that partisan politicking in Washington may prevent the US projecting military power to play its traditional stabilising role in the world.

The good news, the report published by researchers at the US Studies Centre at Sydney University has found, is that key congressional Republicans are pushing for existing resources to be shifted to Asia to tackle problems such as North Korea and China's maritime expansion.

But that is being offset by budget politics that "prevent sensible and strategic defence budget planning", the report states.

"Australia should welcome this sustained military engagement in the Indo-Pacific but remain cautious about Washington's ability to reverse the impact of budget uncertainty on the American armed forces," it says.

Unless Washington's long-running budget impasse can be resolved, "there is a risk that America's global military lead may atrophy".

In a speech to the United Nations this week, Mr Trump ramped up his rhetoric against what he called "a small group of rogue regimes", starting with North Korea and Iran.

Mr Trump's budget request is for $667.6 billion for the next year, an increase of $25 billion, which he has touted as a major boost.

But some congressional Republicans led by Senate Armed Services Committee chairman John McCain and his House counterpart Mac Thornberry, support an increase of a further $30 billion above Mr Trump's pitch. They also want resources shifted to Asian priorities, which the report says shows "commitment to Asian allies in the face of emerging threats to the regional rules-based order and amid uncertainty about the Trump administration's Asia policy".

The new report by researchers Dougal Robinson, Brendan Thomas-Noone and Ashley Townshend states there is now a view among leading defence voices in Congress that unless the budget can be boosted much further, "a mismatch will emerge between US objectives and capabilities".

Mr Townshend told Fairfax Media that Canberra should "take note of the way America's defence budget woes could impact its capacity in the Indo-Pacific, and should actively communicate its concerns to US political actors".

"Australia has a vested interest in an Asian regional order in which the United States remains a capable and forward committed military power.

"As budgetary pressure builds on the US military, Canberra should look for ways to lift some of Washington's regional defence burden in areas of overlapping national interest," he said.

While the White House and Pentagon make budget requests for defence, Congress ultimately decides the final figure and it has been hopelessly gridlocked for several years on the overall national budget.

This story The US vows to get tough with the world's bad guys - but can they afford to? first appeared on The Sydney Morning Herald.