The average credit card interest rate is 21%. The president wants to cap that at 10% for a year.

America loves debt. Uncle Sam currently owes about $38 trillion and change — the change, in this case, being $598 billion — while total household debt in the US has climbed north of $18 trillion, per data from the Federal Reserve Bank of New York.

For households, the majority of those borrowings (some 70%) are tied up in mortgages. However, America’s collective credit card balance is ballooning, an issue that President Trump — who is already on a crusade to lower interest rates across the economy — is now focused on. Taking aim at credit card providers and banks on social media on Sunday, the commander and Truth-Socialer in chief said that Americans were getting “ripped off,” proposing a one-year 10% cap on credit card interest rates, which sent stocks like Visa, Mastercard, and Capital One tumbling in early trading on Monday.

A potential cap on interest rates would be a serious upheaval of financial markets.

While its intentions to stimulate growth and keep more money in the pockets of consumers rather than lenders might be positive, it could unintentionally push vulnerable consumers toward unregulated lenders and limit the availability of credit more generally. If unable to correctly price the risk of lending to a lower-income consumers, banks — not exactly known for their charitable nature — will most likely just stop lending to them altogether.

For now, the consensus among experts seems to be that the proposal is unlikely to make it through Congress, with analysts at Jefferies noting that there’s “no executive authority” to implement such a cap. Nonetheless, it hasn’t stopped traders from selling bank and credit card stocks now and asking questions later.