Greece and US economies are not comparable, Greece uses a foreign currency called the Euro.
US govt debt level and interest rate has a distributive effect (rich get richer) but doesn't impact US govt ability to pay, so this debt 'red alert' stuff is nonsense.
The thing to watch is US interest rates, when they start to fall asset managers will pivot from bonds to stocks, and unemployment, if it gets too high they will pull the brakes off and do QE on the way down.
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