A more thorough explanation:

Shaughnessy v. United States ex rel. Mezei is a legal case that was decided by the Supreme Court of the United States in 1953. The case dealt with the rights of noncitizens seeking entry into the United States.

The Supreme Court held that noncitizens seeking entry into the United States do not possess constitutional rights and may be excluded without a hearing. The Court also held that courts may not temporarily admit such noncitizens into the United States pending arrangements for their departure abroad.

The respondent noncitizen in the case, who had been a resident of the United States for 25 years, travelled to Hungary and stayed there for 19 months. Upon his return, the Attorney General ordered him permanently excluded from the United States on national security grounds without a hearing. The respondent's exclusion on Ellis Island lasted 21 months because other nations refused to accept him.

The case illustrates that noncitizens seeking entry into the United States do not possess constitutional rights and may be excluded without a hearing. The Court's decision was based on Congress' plenary power to regulate immigration, which recognises that the power to expel or exclude aliens is a fundamental sovereign attribute exercised by the government's political departments. The Court held that a noncitizen's Fifth Amendment right to procedural due process differs according to his or her circumstances. Lawful resident noncitizens possess a constitutional right to procedural due process that is not easily removed. However, the constitutional position of noncitizens seeking entry to the United States is different. They have no protections under the Constitution and may be excluded without a hearing.