fate
What evidence is there that the economy is about to "pick up substantially?"
Most indications are that any recovery will be slow, not rapid. Meaning that interest rates are not expected to rise for some time...
Unless, you can point to some other reason why interest rates will rise ...
fate
Can the US borrow more than a trillion a year, print another trillion-plus, and NEVER face any lack of confidence in its currency
Apparently, for the foreseeable future. Because most of the competing economies, and their currencies are also struggling. Those countries that have performed economically better than the US have seen their currencies appreciate, which affects some of their exports (Australia and Canada for instance), but interest rates haven't changed in either country either.
The greatest indicator that countries will start to lose faith in the US, is an increase in the required rates of US treasury Bonds.
But foreign and domestic investors continue to buy US bonds despite the conditions you describe, simply because the US economy and government are seen as a safer bet than most competitor nations, and those that are performing better than the US aren't large enough to offer a sovereign investor too much opportunity to cover...
So, although you are right that a sudden increase in interest rates might create problems for the US, in the short term, (next few years) its very unlikely that interest rates will rise .
Long term, the US still has a lot of positives in its economy. The US has a low median age, which usually predicts growth. The energy deficit is likely to be turned to a surplus, largely by natural gas, but with minor contributions from oil and renewable, and the rising cost of labour in Asian markets is bringing some lower end employment back to the US, Productivity is still high.
On the whole, Fate, deficits aren't a huge worry at this time. Structurally they are a long term problem. But it should be noted that the average Federal taxation to GDP ratio in years when the US has had surpluses is 19.8%. Today its 15%
Right there, you have an indication of why deficits are so large, historically..
The next is that Federal spending is at 25% of GDP. If the economy improves, and spending stays the same, that percentage goes down... Now, I agree that long term the spending does have to come down. By about 5 percentiles of GDP. How much is spending cuts and how much is as a result of growth ?
The problem with cross the board austerity, is that it has proven to stall economies... Without both growth and spending adjustments .... achieving a balance will be impossible. You cannot cut yourself to a balanced budget if it tanks the economy. (The UK has proved that most recently)
fate
Fine, I'll be you. How much would the economy have to pick up for tax revenue to be sufficient to pay for double the current interest? Triple
Moot. Not a scenario that has a chance of occurring.