The US can't just "lock in" rates by deciding to do so. Most of the world treats debt very different than the US consumer is used to on credit-card and mortgage loans.
The US issues debt and the market bids on what it will pay, nearly always charging higher rates for longer terms. And the US can't pay it down early; it has those rates for the entire term of the loan.
Right. In my view it's better to lock in relatively low 10 year (or better yet 30 year) rates rather than roll the dice on interest rates rising. Rates can easily rise to long term norms of 5%.
The market is anticipating that rates will rise, hence the nature of the yield curve.
If the government's assets are long term, shouldn't the liabilities match it?
The US issues debt and the market bids on what it will pay, nearly always charging higher rates for longer terms. And the US can't pay it down early; it has those rates for the entire term of the loan.
If I read http://www.bankrate.com/rates/interest-rates/treasury.aspx?e... right, the US can borrow for 3 months at 0.025%, but for 10 years at 2.63%.
One reason the US does so much short-term borrowing, among other reasons, is that it's so cheap to do so.