After a drumbeat of downgrades, Standard & Poor’s has increased Hartford’s bond rating, but cautioned that the city’s debt is still “vulnerable to nonpayment,” the Hartford Courant reported. The ratings agency bumped Hartford’s rating to CCC, up from CC, following the passage of a state budget that allowed the city — at least for now — to avoid filing for bankruptcy. Mayor Luke Bronin had warned in September that without a state budget, Hartford would be unable to pay its bills within 60 days. His threat of bankruptcy prompted several ratings companies to downgrade the city. Standard & Poor’s issued the rating increase last week, but noted that Hartford’s bonds are still vulnerable to nonpayment because “a default, a distressed exchange or redemption remains possible without a positive development.”