President Biden released his 2024 budget request Thursday while continuing to accuse Republicans of scheming to cut benefits for seniors. But he’s got it backward. By advancing policies that hinder the economic growth that drives prosperity, Mr. Biden and his Democratic colleagues are the ones depriving Social Security and Medicare of the hundreds of billions of dollars those programs need to remain solvent.

I estimate that degrowth policies since 2020 will cumulatively reduce Medicare and Social Security tax revenue by at least $400 billion—and perhaps as much as $900 billion. The tax base will shrink even more if Mr. Biden succeeds in levying higher wealth and business taxes.