So is Antietam and the Monocacy...
It occurred to me to check, and I notice that Gettysburg happens to be considerably north of the Potomac. Based on that, I assume the Potomac was crossable somewhere upriver. Is a turning movement up-around and descending upon the capital from within Pennsylvania completely impossible, or just hard?
So is Antietam and the Monocacy... those didn't work out that well for the rebels, however.
The Potomac is the border between Virginia and Maryland, of course; going all the way to Pennsylvania was something of a challenge for Lee et al in 1863; seems rather unlikely Beauregard and JE Johnston could manage it in 1861.
Here's a map:
You'll note the obvious problem for the rebels trying to go on the offensive after the Bull Run battle - along with McDowell's ~30,000+ in the Defenses of Washington (remember, of course, some 17,000 of which never even moved south of Bull Run and so were able to withdraw into the defenses in good order and with their artillery), there are Mansfield's and Thomas' garrison and militia in the District proper, and then there are another 16,000-18,000 fresh troops under Patterson north and west of the route that Operation REBEL STORM is presumably going to have to take to try and flank to the west of Washington...
Said 16,000, of course, includes 30 regiments of infantry, plus artillery and cavalry, organized into three divisions (1st, Dix; 2nd, Keim; 3rd, Sanford) with brigade commanders that include GH Thomas, Williams, Wynkoop, Negley, Abercrombie, and Stone, among others.
There are also, of course, the troops (USV and militia) available elsewhere in Maryland, as well as in Pennsylvania, which include (among others) the Pennsylvania Reserves.
There's also the minor historical problem that if one looks at a topo map of northern Virginia and southern Maryland, the obvious terrain features include the mountains, hills, rivers, and creeks that a) provide all sorts of ready-made defensive positions, and b) all sorts of channelization effects for a force marching north.
So, impossible in the abstract? No.
In the
reality of July, 1861? Yes, pretty much.
In magical fantasy cavalier land of grey clad chivalry where equally magical rifle bullets fly like guided missiles, though, anything is possible:
"There was a land of Cavaliers and Cotton Fields called The Old South...Here in this pretty world Gallantry took its last bow...Here was the last ever to be seen of Knights and their ladies fair, of Master and of Slave...Look for it only in books for it is no more than a dream remembered. A Civilization gone with the wind."
Best,