In the immediate aftermath of the battle, Lincoln was of course quite pleased with the Union victory and with the commander of the Union forces, Gen. George Meade. However, Lincoln's pleasure soon turned to frustration because he believed that Meade was not being aggressive enough in trying to destroy the Confederate Army. As the ocamh-encyclopdia link below tells us
“We had them within our grasp,” he (Lincoln) lamented. “We had only to stretch forth our hands and they were ours.” He blamed Meade's excessive caution.
As Lee's army began to retreat, many in the North, including Pres. Lincoln, thought that Meade had a great opportunity to destroy Lee more completely. However, Meade was too cautious to attack. Because of this, Lee escaped and Lincoln was left (as he often was) frustrated with the lack of aggression on the part of one of his generals.