Moody’s Investors Service, the only remaining major credit grader to assign the U.S. a top rating, has signaled that its confidence is wavering ahead of a potential government shutdown. While “debt service payments would not be impacted and a short-lived shutdown would be unlikely to disrupt the economy, it would underscore the weakness of U.S. institutional and governance strength relative to other Aaa-rated sovereigns,” analysts led by William Foster wrote in a report Monday. The analysts stopped short of threatening a downgrade, but used unusually blunt language to express their concerns over the trajectory of congressional negotiations to pass a short-term spending bill required to stop a government shutdown when the new U.S. fiscal year begins in October. Markets have been on watch for further credit actions after Fitch Ratings downgraded the U.S. back in August, citing concerns about political wrangling over the debt ceiling that took the nation to the brink of a default. Thus far Congress shows no sign of being able to avoid a shutdown on Oct. 1.