Ambac and MBIA, the two biggest bond insurers, breached an important barrier this week. Soon, none of the main ratings agencies will rate them triple A.

Fitch Ratings, a smaller ratings agency, had already removed their top-notch status months ago. But the biggest agencies still had them at a level which indicated the lowest possible risk of default. Now, Standard & Poor’s has downgraded them to double A status, and Moody’s Investors Service is likely to follow.