The Defense of Marriage Act could be called unconstitutional because it violates the:

A. Full faith and credit clause

B. Amendment 4

C. Amendment 5

D. Amendment 3

C. Amendment 5

Explanation:

The Defense of Marriage Act was a law that defined marriage for legal purposes as the union between a man and a woman, and thus, barred federal benefits and protections for same-sex couples even in states where same-sex marriage was legal.

However, this Act was ruled unconstitutional in the United States v. Windsor (2013) and Obergefell v. Hodges (2015) cases because it violated the equal protection of the laws guaranteed by the Due Process Clause of the Fifth Amendment, which states "No person shall ... be deprived of life, liberty, or property, without due process of law."

This Clause prevents the government from discriminating or providing unequal treatment to Americans, and since the Act was a form of discrimination that viewed same-sex marriages as "second-class marriages" or less worthy for purposes of federal law, it constituted a violation to the Fifth Amendment.