Daily traded volume for US Treasuries is about $500bn.
If there are $100bn of withdrawals tomorrow and banks have to liquidate bonds to provide liquidity for those, then that’s gonna crater T-Bills and push interest rates higher.
So the Fed has stepped in and offered a route for banks to get cash without selling their UST.
Lots of money will move tomorrow, some banks will struggle, but UST should be solid and interest rates and money markets should be insulated.