Final answer:
The death penalty is constitutional in the U.S. because it is allowed under the due process clause of both the Fifth and Fourteenth Amendments, and the Supreme Court case Gregg v. Georgia (1976) upheld its legality by requiring a bifurcated trial process.
Step-by-step explanation:
The death penalty is legal under the United States Constitution primarily for three reasons. First, the Fifth Amendment asserts that no one shall be deprived of life, liberty, or property without due process of law, indicating that as long as the due process is followed, the death penalty can be a legal form of punishment. Second, the due process clause of the Fourteenth Amendment applies this principle to the states, ensuring that they also cannot deprive a person of life, liberty, or property without due process. Lastly, the Supreme Court case Gregg v. Georgia (1976) reaffirmed the constitutionality of the death penalty by introducing a bifurcated trial process, which helped to eliminate the arbitrary nature of capital punishment by separating the guilt and sentencing phases, and thus was found not to be 'cruel and unusual' under the Eighth Amendment.