The new Constitution of the United States, which took effect in March and April 1789, gave the newly organized Congress of the United States authority to establish a federal district up to 10 miles square in size. L'Enfant had already written first to President George Washington, asking to be commissioned to plan the city, but a decision on the capital was put on hold until July 1790 when the First Congress passed the "Residence Act", setting the site of the new federal district and national capital to be on the shores of the Potomac River.