Japan is 13 trillion in debt, while having the economy three times smaller than the US and a shrinking population. Still, it borrows at lower rate than the US.
If it is any indication, we can easily handle 40 trillion in debt.
Notice that is not a qualitative statement in regards to the actual health of their economy? Read and learn:
Japan's Economic Woes Offer Lessons To U.S. | KCUR
First, the government does not spend twice its revenue. Trillion+ dollar deficits started with recession of 2008, but they are coming down as the economy recovers. As for the total debt, see above.
No not that much. More like 25% more. And no the government can not raise revenue on a whim. Not without having a public mutiny. Or perhaps you'll say public bonds. If it were that simple, why haven't they done it?