James Saft is a Reuters columnist. The opinions expressed are his own.

Standard & Poor’s decision to put the U.S. on warning that it may lose its AAA debt rating is both deliciously absurd and genuinely earthshaking.

Absurd because S&P are some of the people who missed the real estate bubble and mortgage bond implosion; and earthshaking because not only has the U.S. never held less than a AAA rating, much less been put on threat of downgrade, it thoroughly deserves the warning.

Standard & Poor’s cited the risks of a lack of a credible plan to reduce the national debt and said the move flags a one-in-three chance of a downgrade over the coming two years.

The ratings agency said there was a material risk policymakers won’t come to a meaningful and plausible budget agreement by the 2012 elections, leaving the U.S. weaker than its AAA-rated peers.

Beyond the risk of a lack of political will to tame the budget, S&P also raised the fiscal threats coming from the financial sector, which it now puts as higher than before 2008. So much for financial reform, then. Net external debt, a measure of U.S. dependence on foreign creditors, is now at 300 percent of current account receipts, among the highest of any sovereign, much less those that consider a AAA rating to be something akin to a birthright.