Tyler Cowen:

Many on the left are boasting that the U.S. government could borrow lots more (look at the current T-Bill rate), forgetting they used to warn us that international capital flows, as amplified through noise traders and speculators, mean that crises can arrive in a single, whiplash moment, bringing countries from riches to rags virtually overnight.  Somehow those old narratives are being forgotten, I wonder why.

Willem Buiter has a longer explanation.