Close as he was to the enemy he had almost no idea of what they were doing

 From 1776 by David McCulough. Page 268.

But of this Washington seems to have known little or nothing. Close as he was to the enemy he had almost no idea of what they were doing, no knowledge that Howe and Cornwallis had departed, and that neither he nor Congress were any longer under immediate threat.

“The Delaware now divides what remains of our little force from that of General Howe whose object, beyond all question, is to possess Philadelphia,” Washington wrote on December 18, four days after Howe’s departure, to James Bowdoin, a member of the Massachusetts Council. Were the river to freeze, Washington feared, the enemy might attack over the ice. “Strain every nerve for carrying out the necessary works,” he told Israel Putnam, who was charged with the defense of Philadelphia. “There seems to be the strongest reason to believe the enemy will attempt to pass the river as soon as the ice is sufficiently formed.”

Desperate for reliable intelligence—for information of almost any kind—Washington let it be known he was willing to pay for it, at almost any price. In a dispatch to his general officers, he implored them to find a spy who would cross the river and determine whether any boats were being built or coming overland. “Expense must not be spared in procuring such intelligence, and will readily be paid by me.” To Lord Stirling, he wrote, “Use every possible means without regard to expense to come with certainty at the enemy’s strength, situation, and movements—without this we wander in a wilderness of uncertainties.”

As early as December 15, he had received a report from a commander of Pennsylvania militia posted below Trenton, John Cadwalader, saying, “General Howe is certainly gone to New York, unless the whole is a scheme to amuse and surprise.” Perhaps Washington found it impossible to believe, or suspected that it was indeed a ruse. Whatever the reason, he seems to have ignored it.

The foe gathered on the other side of the river was the British army no longer, but a holding force of 1,500 Hessians settled in for the winter under the command of Colonel Johann Rall, the veteran officer who had led the fierce Hessian assaults at White Plains and Fort Washington.