Within hours of his inauguration, President Donald Trump signed an executive order that would withhold U.S. citizenship from the children of some immigrants born in the United States, calling the order a “big one.” The executive order would end a right that the U.S. Constitution has guaranteed for more than 150 years.

On the Fourth of July, beneath a sun that seemed to soften just in time for the ceremony, one hundred immigrants reminded the crowd of the enduring allure of American citizenship as they swore their allegiance to the United States.

Amid the uncertainty and potential changes in the naturalization process to be a U.S. citizen, here are five things to know.

In 1967, the Supreme Court said the government usually cannot take away citizenship without a person’s consent.

The president’s executive order denies citizenship to individuals born to parents living in the U.S. illegally or temporarily.

Birthright citizenship is specified by the 14th Amendment to the U.S. Constitution-"All persons born or naturalized in the United States"-and interpreted plainly by 150 years of Supreme Court precedent.