When that reprobate General Sickles moved his men out of position at Cemetery Ridge, against orders, and the bold Mississipi general (name escapes me) moved to capitalize on the mistake, if not for Wisconsin’s LTC Dawes filling the breech, the Union’s supply line (and escape route, Baltimore Pike?) would have been cut.
“Pickett’s charge” is where US artillery earned the title `King of Battle.’
But for that there would have been nothing standing between Lee’s army—Lee admittedly bled but never timid like a string of dismissed federal brass hats—nothing between him and Washington DC but routed Yankee troops.
I can see the Union having to sue for peace if Lincoln were then captured. Check mate, CSA.
And the forts and garrison of Washington, which was probably larger than his army at that point.
Lee’s Army of Northern Virginia continued on as a formidable fighting force after being defeated at Gettysburg. Why would not have Meade’s Army of the Potomac done the same? Keep in mind that the AOP had prepared defensive lines in MD as a fallback position in case things went poorly at Gettysburg. Besides the DC fortifications, Lee likely would have had to fight the AOP again to reach DC.