In early December 1776, Washington's army was forced to retreat across the Delaware River and into Pennsylvania, and most members of Congress temporarily left Philadelphia. Morris was one of few delegates to remain in the city, and Congress appointed Morris and two other delegates to "execute Continental business" in its absence. Morris frequently corresponded with Washington, and he provided supplies that helped enable the Continental victory at the Battle of Trenton. After the Continental Army was defeated in the September 1777 Battle of Brandywine, Congress fled west from Philadelphia; Morris and his family went to live at the estate they had recently purchased in Manheim, Pennsylvania. Morris obtained a leave of absence in late 1777, but he spent much of his time defending himself against false attacks regarding alleged mismanagement and financial improprieties levied by the pro-slavery allies of Henry Laurens, the president of the Continental Congress. Due to his leave of absence, Morris did not play a large role in drafting the Articles of Confederation, which would be the first constitution of the United States, but he signed the document in March 1778. As some states objected to the Articles, it would not enter into force until 1781.