He was one upon whom to rely in the proposed scheme of fortifying the city, and his long experience at entrenching made him peculiarly fit for the work.
His sturdy nature, good sense, and ready wit made him at once a favorite with the Continental Congress and the Committee of Safety; though the former, acting on his advice, soon left the city for the greater security of Baltimore.

Putnam soon placed the city under martial law, drafted all the citizens, except the Quakers, into the military service, and put the place in the best posture for defense of which it was capable.

"There were foes within the city as well as foes without," for the Tory element was strong in Philadelphia, and it was because of it that Putnam was unable to cooperate with Washington when he dealt the enemy the first of those telling blows at Trenton and Princeton.

He dared not withdraw his men from the city, even for a short absence, in order to create a diversion while his Commander-in-Chief made the direct attack.

Had he done so, and also the other generals to whom were entrusted the details of this affair, the Hessians might have been entirely cut off in their retreat from Trenton and practically destroyed.