Every court in the United States from municipal traffic court to a state court to a U.S. District Court has both the right and the obligation to consider claims of unconstitutionality just like any other legal question that a case presents. Contrary to popular misconception, constitutional law issues are not the exclusive province of the U.S. Supreme Court. Indeed, constitutional issues are only ruled upon in the first instance in the U.S. Supreme Court (or even in a direct appeal from a trial court to the U.S. Supreme Court) in rare and isolated cases. Usually, at least one trial court judge and at least three appellate court judges, and often more appellate court judges, have ruled upon a constitutional issue before the U.S. Supreme Court considers it.
This is just as true in Louisiana and Puerto Rico, which have legal systems based upon the civil law legal system, as it is in other U.S. jurisdictions, which have a common law legal system.
There is usually only one difference between a case in which the constitutionality of a statute is called into question and one in which it is not. When the constitutionality of a statute is called into question, many state and federal rules of civil procedure require or permit the attorney general of the state whose statute's constitutionality (or the U.S. attorney general when a federal law's constitutionality is at issue) to be joined as a party for the purpose of litigating that issue. This allows the court to receive arguments on the constitutional issue from the public's perspective as well as the perspectives of the parties.
A few states also provide that appeals from trial court decisions finding that a statute is unconstitutional are directly to the state supreme court, rather than to the intermediate court of appeals as they would usually be in those states.
Notably, the distinct treatment of constitutional issues in many civil law systems is not inherently a part of the civil law system. Constitutional courts are mostly a post-World War II constitutional innovation in the countries where they are found.
For example, the "law-screen" doctrine and the existence of a constitutional court in France, is much younger than core of the rest of the civil law system in France, which invented the civil law system in its modern form more than two hundred years ago. Neither France, at the time Louisiana adopted its civil law legal system through the time of the Louisiana Purchase, nor Spain at the time that Puerto Rico was ceded to the United States after the Spanish-American war, had constitutional courts.
Footnote Regarding Treaties
Also, it is worth remarking that in Europe and much of the rest of the world, the function of protecting individual rights against government authority in a way that is entrenched so that it is not easily overcome by domestic legislation of a current political regime is accomplished through international treaties, rather than only through entrenched rights in a constitution as they are in the United States. Although even then, in many European countries, ordinary courts apply only domestic law and the country in question has to adopt domestic law to conform to the treaties.
This treaty mechanism is not very effective in the U.S., because in the U.S., unlike most countries, an ordinary domestic law can override an earlier adopted and ratified international treaty.