Supporting the military is always a political winner.

On 9 February 2018, President Donald Trump signed into law the biggest year-to-year increase in defence spending since 2003.110 News outlets and commentators were quick to declare the Bipartisan Budget Act of 2018 (BBA) “a Pentagon budget like none before”,111 characterising the increase to defence spending as “the upper limit of what anyone thought was possible”.112 This language was not entirely hyperbolic: Congress defied years of convention by providing more funds for defence in the BBA than requested in the president’s budget, in an agreement that dwarfed the rate of past increases to Budget Control Act (BCA) spending limits by more than three times over.113 While previous legislative deals to soften the impact of the BCA had been relatively modest, the BBA added US$80 billion to defence spending in FY2018 and $85 billion in FY2019 — representing a real increase of approximately 11 per cent.114 This year Congress has passed another bipartisan spending deal to cover the remaining two years of the BCA. Under this agreement, spending on defence is set to reach US $738 billion in FY2020 and US$740.5 billion in FY2021, a comparatively modest increase that shrinks to a flatline with inflation from the following year.115 Both of these short-term political fixes, however, obscure longer-term barriers and evolving partisan dynamics in Congress that will prevent sustained and predictable budget increases of a similar scale in the future. Rather than heralding a new era for US defence spending, they illustrate an overdue attempt by legislators to offset some of the damaging results of spending limits imposed by the BCA. Importantly, they do not form a model for spending agreements following the expiration of these caps in 2021 and beyond.∂ Between 2011 and 2018, total spending on US national defence declined in real terms by 21 per cent.116 In the lead-up to the passage of the BBA, a targeted campaign by the late Senate Armed Services Committee Chairman John McCain (R-AZ) and then-House Armed Services Committee Chairman Mac Thornberry (R-TX) brought home the reality of America’s military readiness crisis to lawmakers, successfully linking defence spending cuts with a string of US Navy collisions at sea.117 Republican defence hawks were able to capitalise upon political momentum to raise spending in a crucial midterm election year, when their party had unified control of government and was keen to deliver a key election promise made by President Trump. Democrats, for their part, were motivated by a desire to deliver a “win” to their political base from a position of relative legislative weakness by demanding comparable increases to domestic spending in return for their support.118 Yet, even following his successful stewardship of the deal, Thornberry was quick to warn “it would be a mistake” to view the BBA as a silver bullet for the Pentagon, stating that “not everything is fixed because we have a substantial increase in one year” and quipping “the closer you look, the deeper the problems are”.119 Many of these problems are deeply ingrained. The US defence budget has faced significant downward pressure and decreased buying power over the past decade. As the National Defense Strategy Commission report shows, even factoring in the US$237 billion of cumulative defence funding added by the BBA and two previous budget deals in 2013 and 2015, BCA-imposed spending caps have still resulted in a net US$539 billion reduction in base budgets between 2012 and 2019, relative to former Secretary of Defense Robert Gates’ final spending plan before the BCA became law.120 While the US$700 billion of enacted defence spending resulting from the BBA in FY2018 was a significant increase from the previous fiscal year, growth in the budget’s top line to US$716 billion in FY2019 was on par with inflation and has by no means undone the damage of cumulative spending shortfalls since 2011.121∂