There's a key tool hiding in plain sight: the mortgage portfolios held by Fannie Mae and Freddie Mac. Here's how it works—these two government-sponsored enterprises operate under specific agreements with the U.S. Treasury, and there's a hard cap on what they can hold. The limit? $225 billion per company in mortgage investments. That's it. Both entities are sitting close to those ceilings, which matters more than most realize. When portfolios hit the limit, it creates a ripple effect through the entire financial system—less liquidity flowing into mortgage markets means capital gets redirected elsewhere. For macro watchers and traders tracking systemic liquidity, this constraint becomes surprisingly important. The mechanics are straightforward but the implications ripple outward.