The Policy Won't Hold Up Under Strict Scrutiny
The Trump administration is hell bent on enforcing its immigration and refugee ban. The ban would ultimately a temporary ban on the inflow of Muslims into the United States, however we cannot truly know what Trump means when he says temporary. The language of the ban does not explicitly discriminate against Muslims and the Islamic faith, but the intent behind the ban and the potential effect of the ban are to explicitly discriminate against Muslims and Islam.
The Supreme Court is likely to view this case in regards to the religious clauses of the First Amendment. These clauses are the free exercise of religion clause and the establishment of religion clause. The former concerns an individual's right to practice their religion as they see fit, while the latter concerns government support for religion and/or the disadvantaging of religion by the government. The constitution applies first and foremost to the government itself, so the nature of whether or not those affected are always American citizens does not matter. All levels of government, be they federal, local, or state, cannot support or disadvantage the establishment of religion nor can they restrict the free exercise of religion.
The Trump administration's Muslim ban concerns both clauses of the First Amendment regarding religion, not just one.
It restricts the travel of individual Americans almost solely based upon their religion. While there is no explicit discriminatory language within the policy, the only group to be truly impacted by the travel ban will be Muslims. Trump has explicitly stated that he believes Muslims and Islam itself are a problem and threat He and the American right base this belief purely upon anecdotal evidence and stereotypes about the faith and its followers. This type of policy infringes upon the individual's right to free expression as guaranteed by the constitution.
The ban also manifests itself as a government matter favoring or disadvantaging the establishment of religion. The intent behind the policy is to restrict the entry of the Islamic faith into the United States by banning the entry of Muslims into the country. That intent itself creates a situation where the federal government is explicitly attempting to disadvantage a specific religion, Islam, and favor other religions.
The constitutional standard that the Supreme Court will likely apply to this case is something call strict scrutiny. The strict scrutiny standard requires that government policy that infringes upon constitutional rights exists to further a compelling government interest and is narrowly tailored to achieve said interest.
The Trump administration's arguments will likely say the compelling interest is national security, a time honored compelling government interest. The issue with the policy comes down to whether or not the policy is narrowly tailored. The administration likely anticipated this standard and so built the ban to be "temporary" and focus on Muslim majority nations as opposed to Muslims themselves. This does not change the intent nor the effect of the legislation. The rhetoric surrounding the policy has clearly shown that the ban exists to negatively impact the Muslim community and Islamic faith.
The Muslim ban clearly fails the test applied by the standard of strict scrutiny and therefore violates the religion clauses of the American constitution's First Amendment.
The First Amendment exists to prevent policy such as this from existing.