There will not always be a buyer of another t-bill. What do you think is going to happen when the baby boomers start retiring? Social Security, Medicare, Medicaid all trying to support a glut of population that did not build up a pile of savings, but rather a pile of debt. The Net Present Value (value of future payments deducted for the interest amount) of the US future payments is over 50 Trillion dollars, before the bailouts. That means you would have to have that amount saved, today, earning interest to be able to afford all those programs.
Some governments actually do this. Canada, for example, can "pull out the key" of its CPP (Social Security equiv.) and everyone will get out at least what they put in. Not only that but Canada has been paying off its debt for the past 14 years. To prepare for the influx of medical patients Canada is building hospitals all across the country so that when patients actually start coming they can stop building hospitals and start fully running them, without having to find too much extra capital.
Where do you think a smart hacker will locate once the baby boomers start to age? In a country that saved and prepared that can keep taxes medium or a country that needs to ratchet them up to pay for their old people?