Kansas City, Kan.

ON Friday, Gov. Jan Brewer of Arizona signed a law  SB 1070  that prohibits the harboring of illegal aliens and makes it a state crime for an alien to commit certain federal immigration crimes. It also requires police officers who, in the course of a traffic stop or other law-enforcement action, come to a “reasonable suspicion” that a person is an illegal alien verify the person’s immigration status with the federal government.

Predictably, groups that favor relaxed enforcement of immigration laws, including the American Civil Liberties Union and the Mexican American Legal Defense and Education Fund, insist the law is unconstitutional. Less predictably, President Obama declared it “misguided” and said the Justice Department would take a look.

Presumably, the government lawyers who do so will actually read the law, something its critics don’t seem to have done. The arguments we’ve heard against it either misrepresent its text or are otherwise inaccurate. As someone who helped draft the statute, I will rebut the major criticisms individually:

It is unfair to demand that aliens carry their documents with them. It is true that the Arizona law makes it a misdemeanor for an alien to fail to carry certain documents. “Now, suddenly, if you don’t have your papers ... you’re going to be harassed,” the president said. “That’s not the right way to go.” But since 1940, it has been a federal crime for aliens to fail to keep such registration documents with them. The Arizona law simply adds a state penalty to what was already a federal crime. Moreover, as anyone who has traveled abroad knows, other nations have similar documentation requirements.

“Reasonable suspicion” is a meaningless term that will permit police misconduct. Over the past four decades, federal courts have issued hundreds of opinions defining those two words. The Arizona law didn’t invent the concept: Precedents list the factors that can contribute to reasonable suspicion; when several are combined, the “totality of circumstances” that results may create reasonable suspicion that a crime has been committed.