This would have been an appropriate headline for an article about warnings from S&P and Moody's that they might downgrade U.S. debt. These credit agencies rated hundreds of billions of dollars worth of mortgage backed securities that were backed largely by subprime and Alt-A loans as investment grade. Of course they were paid large amounts of money by investment banks for these ratings.
It would be appropriate to provide readers with background information so that they can better assess these sorts of warnings. It also is worth noting that Japan's debt was downgraded by S&P back in 2001 and in 1998 by Moody's. The interest rate on Japan's 10-year Treasury bonds is currently a bit over 1.0 percent. Clearly the downgrading by these credit rating agencies have not had much effect on Japan's ability to borrow.