Any attempt to impugn the character of prosecution witnesses was ruled slander by the court. The prosecution did its best to impugn Milke's credibility. Some of these critics have attempted to impugn the motives of the earliest reviewers. To impugn a contract means attacking the integrity of the contract. To impugn his opponents' competence, he answered them with the texts they themselves had cited. The defendant can impugn the decree within fifteen days of the service of the decree.