Most treasuries were held by the U.S. government itself, particularly the Social Security Trust Fund. But the trust fund has now switched to net withdrawal of i

Most treasuries were held by the U.S. government itself, particularly the Social Security Trust Fund. But the trust fund has now switched to net withdrawal of its savings, which means the total outstanding debt will increasingly be held by commercial and foreign ownership, rates may increase, and, worse, become more volatile as the Trust Fund won't be there as a cushion. The upshot is that the ability of the U.S. to fund and service debt will become increasingly vulnerable to the global economy. One reason why demand for U.S. treasuries are so high is because it was cushioned from global economic forces. The U.S. was a safe haven. Debt-to-GDP ratio is important as an indicator of your ability to weather global slowdowns and remain in control of domestic budgeting. So what the future brings is accelerating volatility as the forces which conspired to keep rates stable and low will begin to conspire to do the opposite. Whether rates become burdensome long-term depends on many factors, but the increased volatility alone could be hugely disruptive and costly.