On May 14, the Supreme Court overturned the Professional and Amateur Sports Protection Act, which largely prohibited sports betting outside of Nevada, saying the law was unconstitutional.

“It is as if federal officers were installed in state legislative chambers and were armed with the authority to stop legislators from voting on any offending proposals,” Justice Samuel A. Alito Jr. said, writing for the majority. “A more direct affront to state sovereignty is not easy to imagine.”

With its decision, the Supreme Court opened the door to legalize an estimated $150 billion in illegal wagers on professional and amateur sports that Americans make every year.

“Crushing the illegal market” is crucial, Sara Slane, a senior vice president at the American Gaming Association, a trade group that represents casinos, said on Tuesday. “Delaware being the first mover certainly puts more pressure on other states to compete.”