While there were no Union Army forces between lee’s Army and Washington, other than the Army of the Potomac, there were 95,000 Union soldiers manning 44 forts with over 500 big artillery pieces defending Washington. It is very doubtful lee could have forced the Lincoln administration to sue for peace. Longstreet did not council Lee to move on Washington. Longstreet recommended they break off action with the Army of the Potomac, move the army to a more defensible location and force the Union Army to attack them. This is the same advice that he gave to General Lee in late May before the Gettysburg campaign started. Lee at that time stated his plan was to find suitable ground in Pennsylvania and attack the Army of Potomac there.
All very true. Thanks for the insight and correction.