The US treasury takes in $14.5 BILLION every day, day in, day out. That is around $500 million in taxes every hour. All they have to do is prioritize the payouts. Why is it all or nothing?
It's the way the Constituion made it. Congress holds the purse strings. Appropriations are mostly annual. No appropriation, no money can be spent (see Anti-deficiency act of 1884). Mandates (social security and Medicare/Medicaid are not appropriations. Therefore they have to be paid. No annual appropriation bill is required. If anyone is claiming that SS/Medicare/Medicaid is impacted, they're full of it. But everything else is. They cannot spend money they have no appropriation to spend. Even if treasury is bringing in that much per day.