What is the burden of proving a person's citizenship?

The district court found the petitioner had carried his initial burden of proof by offering a U.S. passport and showing that his wife and children had adjusted status and obtained citizenship through him. MondacaVega v. Holder, No. 2:04cv00339FVS, 2011 WL 2746217, at *9 (E.D.Wash. July 14, 2011). The court then shifted the burden to the government to rebut the petitioner's claim of citizenship by "clear and convincing" evidence, and, after hearing the government's case, found this burden satisfied. Id. at *910. This conclusion was based in part on the district judge's finding that the petitioner's testimony was not credible. Id. at *78, *10.