Final answer:
The U.S. Constitution's application of equal protection and protection from 'cruel and unusual punishments' have not always preserved justice equally, due to interpretations of the Fourteenth and Eighth Amendments, and the cautious expansion of liberties by the judicial branch.
Step-by-step explanation:
An element of the U.S. Constitution that has not always been successful in preserving the principles of justice is its application of the equal protection clause of the Fourteenth Amendment. Although this amendment promises equal protection under the law, historically, certain groups have experienced discriminatory treatment by the justice system, which contradicts this principle. One example includes the inequitable application of bail, where similar circumstances have not always resulted in fair treatment, thus impacting the principle of equality before the law.
The Eighth Amendment also aimed to ensure a justice system free from 'cruel and unusual punishments'; however, issues like the death penalty continue to challenge the interpretation and application of what constitutes cruelty, demonstrating the dynamic nature of constitutional rights and their enforcement.
Despite these protections, the judicial branch has often acted cautiously in expanding liberties, balancing individual rights with governmental interests, which occasionally leads to an evolutionary, rather than instantaneous, advancement of justice.