Public spending programmes, once established, become entrenched, making it hard for the next administration to cut them. For many, this inertia leads to bloated spending and makes debt unsustainable. This column argues that the link between budget inertia and fiscal sustainability is surprisingly not straightforward. It examines when fiscal reforms might be ineffective, showing that inertia may improve fiscal sustainability – especially when coupled with more consensual legislative decision-making. In the case of the US, it argues that enforcing the Senate’s 60% supermajority rule would lower US debt. […]