Also, at the worst.
In the least favorable circumstance; under the most difficult conditions. For example, Convicted of taking a bribe, the official believed that at worst he would be sentenced to a few months in prison. [1500s]
In the least favorable view or supposition, as in No harm done; at the worst I'll copy the tax return again. Chaucer used this sense in Troilus and Cressida: "For at the worst, it may yet short our way." [Late 1300s] For the antonym, see at best.