It's the spending

Wall Street Journal: "How the U.S. Went $40 Trillion in Debt - The problem isn’t tax cuts. Spending is way above historical norms."

Gross national debt has increased $17 trillion since 2019. That’s about as much debt as the U.S. added during the entire first 225 years of its history. While the liberal press blames the GOP’s 2017 tax cuts, and their extension in last year’s One Big Beautiful Bill, revenue has increased 68% since 2018. That’s twice the rate of inflation.

Since 2018, revenue has averaged about 17% of GDP, roughly the historical norm. Yet spending has averaged slightly over 24% of GDP, versus a pre-pandemic historical average of 20%.

The revenue-to-GDP statistic is a hard ceiling that does not change that much whether tax rates are high or low.  You simply can't get much above that historical level.  Spending, on the other hand, can fluctuate wildly based on war or pandemics or other crises.  The trick is pulling back spending when the crisis passes.