The phrase "is one's case" is often used to describe a situation where someone has presented their argument or evidence in support of a particular belief or action. Antonyms for this phrase might include "disproven," "refuted," or "discredited," which suggest that evidence has been presented that discredits or undermines the original argument. Other antonyms might include "ignored," "dismissed," or "discounted," which suggest that the argument has been overlooked or given little weight in the overall decision-making process. Overall, the phrase "is one's case" implies a sense of support or justification, while its antonyms suggest the opposite.