Share of budget is actually a terrible way to look at this because the budget itself has exploded, and that ratio hides most of the real modern risk.

Interest costs in the 80s spiked because high rates were applied to a much smaller debt base. Today we have the opposite problem: rates that are high compared to the 2010s are now rolling onto a massively larger stock of debt. We’ve only just started to refinance that debt at the new levels, so the full impact hasn’t even shown up yet. We are still seeing significant inflation (meaning rates still have upwards room to grow), beginning signs of an economic pullback, are beginning to see signs of a Fed unwilling to raise rates sufficiently due to the impact on the fiscal environ, etc.