coltshooter1,
I'm trying hard to make your original 'what if' premise work — that Early actually gains access to Washington, DC — but it's really difficult.
The city is ringed by approximately 50-60 forts of varying sizes, and the city itself is garrisoned by about 20,000 troops (albeit mostly new recruits and heavy artillerists, I think, along with the recuperating invalids and wounded from other battles).
http://www.nps.gov/archive/rocr/ftcircle/
Early, meanwhile, approaches with about 10,000-13,000 troops and had already suffered a day's delay by Lew Wallace's dogged defense at the battle of Monocacy. That probably should have suggested something to Early.
Grant sends two regiments of the 6th Corps — about 5,000 veterans from the ongoing siege of Petersburg — as reinforcements.
Early's purpose was to draw troops away from Grant, and in that he succeeded. By the same token, I'm doubtful that Grant hardly missed those troops. And, I'm not convinced Early's primary objective was to actually take the city anyway as much as to threaten it.
Early taking 13,000 men to take the most heavily defended city on the planet at that time just does not compute.
But, to address your original 'what if', if by some happenstance Early does break through, I think it becomes the equivalent to Armistead's 'breakthrough' at the copse of trees or Gordon's attack at Fort Stedman — initially successful, but quickly swallowed up for lack of support.
And to address your second thought, I don't see where Early could have gone other than DC to provoke Grant to release more troops. To me, Early just wasn't strong enough to be anything more than an annoyance.
Besides, doesn't Early's presence result in the creation of the Army of the Shenandoah under Sheridan a month later? Early had no realistic chance, IMO.