Attorneys general from 22 states sued President Trump today to block a new executive order he signed declaring that children born to undocumented immigrants would no longer be treated as citizens.

The order would extend even to the children of some mothers who are in the country legally but temporarily, such as foreign students. The states argued that the order violated the 14th Amendment, which courts have long interpreted to guarantee citizenship to every baby born in the U.S.

The lawsuit is just the beginning of what is expected to be a long legal battle over the president’s crackdown on immigration. Trump also directed the military to play a role in border control, which legal experts said would clash with the law. At the border, migrants realized they now have few options.

Dozens of other executive orders signed by Trump in his first-day blitz have also begun to reverberate around the country. Trade policy experts scrambled to understand Trump’s tariff plans, automakers confronted an assault on their electric vehicle programs and the wind power industry faced potentially crippling restrictions.

At an interfaith service today in Washington, a bishop urged Trump to “have mercy upon the people in our country who are scared now,” specifically naming L.G.B.T.Q. people, immigrants, children and people fleeing war zones. Afterward, the president appeared unmoved, telling reporters, “Not too exciting, was it?”