A. Three standards: There are three key standards of review which reappear constantly throughout Constitutional Law. When a court reviews the constitutionality of government action, it is likely to be choosing from among one of these three standards of review: (1) the mere-rationality standard; (2) the strict scrutiny standard; and (3) the middle-level review standard. 
1. Mere-rationality standard: Of the three standards, the easiest one to satisfy is the “mere-rationality” standard. When the court applies this “mere-rationality” standard, the court will uphold the governmental action so long as two requirements are met:
a. Legitimate state objective: First, the government must be pursuing a legitimate governmental objective. This is a very broad concept — practically any type of health, safety or “general welfare” goal will be found to be “legitimate.”
b. Rational relation: Second, there has to be a “minimally rational relation” between the means chosen by the government and the state objective. This requirement, too, is extremely easy to satisfy: only if the government has acted in a completely “arbitrary and irrational” way will this rational link between means and end not be found.
2. Strict scrutiny: At the other end of the spectrum, the standard that is hardest to satisfy is the “strict scrutiny” standard of review. This standard will only be satisfied if the governmental act satisfies two very tough requirements:
a. Compelling objective: First, the objective being pursued by the government must be “compelling” (not just “legitimate,” as for the “mere-rationality” standard); and
b. Necessary means: Second, the means chosen by the government must be “necessary” to achieve that compelling end. In other words, the “fit” between the means and the end must be extremely tight. (It’s not enough that there’s a “rational relation” between the means and the end, which is enough under the “mere-rationality” standard.)
i. No less restrictive alternatives: In practice, this requirement that the means be “necessary” means that there must not be any less restrictive means that would accomplish the government’s objective just as well.