A federal appeals court on Wednesday upheld the most contentious provision of the health-care overhaul law, ruling that Congress can require Americans to carry insurance coverage. In backing the individual mandate, the U.S. Court of Appeals for the 6th Circuit in Cincinnati became the first appellate court to rule on President Obama’s signature domestic initiative. The decision also marked the first time a Republican-appointed judge has sided with the administration in evaluating the law’s constitutionality. “We find that the minimum coverage provision is a valid exercise of legislative power by Congress under the Commerce Clause,” Judge Boyce F. Martin Jr., a Democratic appointee, wrote for the majority. He was joined by Republican appointee Jeffrey Sutton.