I didn't see any of the claims that "McClellan wanted to continue the campaign as soon as possible.........." In fact the opposite is what's in his own
Report McClellan only wanted the bridge to defend HF. From his base at HF if he went the Shenandoah route he didn't expect to reach beyond Winchester after the Potomac had crested and the fords unavailable. This would have been in late October. As has already been posted in a previous post Halleck wanted McClellan to cross the Potomac after Lee on Oct 1st. Besides this you have raised the issue that McClellan raised (among many others) that held him back; supply shortage. Another thing to consider that Halleck pointed out is that the bridge would take 3-4 weeks to build. McClellan was requesting the
bridge to be built on October 1st. When McClellan finally sends the plan to the
Shenandoah route he adds that he can't advance past Winchester, needs at least three more days before three of his Corps can move, additional reinforcements because "it would be a desperate affair" if battle at Winchester. This doesn't appear as someone who's eager to get anything started soon.
I know McClellan pointed out that the bridge was necessary to defend Harpers Ferry
even if it wasn't used offensively, so they may as well build it as soon as possible even if Lincoln wanted him to move along a different route.
As for "finally", the timeframe doesn't seem to me to support "finally".
From 67th's write-up of the subject.
September:
On the 22nd, Sumner was
ordered to throw a pontoon bridge over the Potomac, and occupy the far side. McClellan
wrote to the President of the C&O Railroad to send construction teams to rebuild the rail bridge, and also to Halleck to have him authorise the expense. On the 23rd Halleck asked McClellan's intent, and on the 24th McClellan
replied he was going to cross the Potomac and Shenandoah, and attack Winchester. McClellan noted the storm assisted them by making it impossible for Lee to cross the Potomac, whereas he could use the rebuilt bridges at Harper's Ferry. Halleck had also previously stated the 11th Corps would be released to McClellan, and on the 25th McClellan suggested the 11th Corps march to Knoxville (i.e. where the Potomac cut through South Mountain). On the same day, McClellan gave his plans to his wife; essentially he intended to let the Potomac rise (as it already was) to prevent Lee fording the river, then use the rebuilt bridges to attack Winchester. This is exactly what he told Halleck.
On the 26th, the hammer falls on the campaign. In one
telegram, Halleck states he will not send any more troops until McClellan's plans are "agreed on", and that he believes there is a whole other rebel army waiting to strike Washington. In
another, Halleck denies the requisition for the repair of the Harper's Ferry bridges until he agrees to McClellan's plans. This effectively ends the plans for immediate forward movement. Halleck has imposed control measures to stop McClellan from advancing.
(section skipped)
1st October:
On 1st October, McClellan
writes to Halleck that the permanent occupation of Harper's Ferry is "taken for granted" by him, and without reference to future operations, the bridges are needed, if only for the proper defence of the place. Halleck's reply is that he cannot authorise the expenditure, only the President can, and he is
en route. He states that the delay caused by rebuilding the bridges would be unacceptable. Hence Halleck decides to delay more, by refusing to get the work started.
That afternoon, Lincoln showed up unannounced at Harper's Ferry, having traveled by train, but having to disembark early (at Monocacy), travel down to Harper's Ferry in a carriage and cross the rivers by the pontoon bridges, because the main bridges had still not yet been repaired. McClellan rode down to see him, and Lincoln spent four days with the army. The consultation on further actions occurred on the 4th October, and was during a ride to South Mountain. McClellan recorded an immediate impression that he had convinced Lincoln of the problems with advancing before preparations (i.e. the bridges) were complete, and
Stotelmyer found two additional confirmatory accounts. This seems to be true, as the next day Halleck orders Cox's division removed from McClellan's army. Deliberately weakening McClellan's army would not be done if McClellan was intended to take the offensive by Washington.
(short section skipped)
On the morning of the 7th October, this apparent understanding is shattered. The following
telegram from Halleck is received:
"I am instructed to telegraph you as follows: The President directs that you cross the Potomac and give battle to the enemy or drive him south. Your army must move now while the roads are good. If you cross the river between the enemy and Washington, and cover the latter by your operation, you can be re-enforced with 30,000 men. If you move up the Valley of the Shenandoah, not more than 12,000 or 15,000 can be sent to you. The President advises the interior line between Washington and the enemy, but does not order it. He is very desirous that your army move as soon as possible. You will immediately report what line you adopt and when you intend to cross the river; also to what point the re-enforcements are to be sent. It is necessary that the plan of your operations be positively determined on before orders are given for building bridges and repairing railroads.
I am directed to add that the Secretary of War and the General-in-Chief fully concur with the President in these instructions.''
This telegram is often mis-quoted. Some parse it as an order for an immediate movement (even Lincoln, two years later, recalled that he'd issued a peremptory order, which he clearly hadn't). However, the bolded sentence reveals that it is not. Washington's control measures are still in place, and they wish to approve any action before it is undertaken.
(what follows is mine)
McClellan replies to Halleck immediately, by the way. What he says, summarized, is that McClellan thinks that the strike into the Shenandoah will either result in a fight around (or north of) Winchester, or (and presuambly more likely) it will result in Lee having to abandon the northern part of the Valley.
Thus, while McClellan can't fight Lee much south of Winchester, this doesn't actually matter because McClellan's objective is simply to drive Lee south of Winchester and
then plan future operations.
If we have a look at the position map:
The numbers are what's important here. If Lee is still positioned with half his troops at Martinsburg and the other half at Winchester, then McClellan can't pull 5th and 6th Corps away from the upper Potomac while it's still possible to cross the upper Potomac - otherwise he's exposing the North to immediate invasion.
There are effectively three ways in which this problem can be resolved:
1) McClellan can be given enough troops that he can leave 5th and 6th Corps covering the upper Potomac and still go on the offensive east of the Blue Ridge Mountains (down into Loudoun Valley). In this situation then he doesn't care about leaving 5th and 6th Corps where they are because if Lee
does come down to fight him he doesn't need them to have an advantage.
2) McClellan can attack into the Shenandoah and force Lee to pull back south of Winchester. In this situation then McClellan no longer needs to leave multiple corps covering the upper Potomac, and can then go on the offensive east of the Blue Ridge mountains.
3) McClellan can wait until the Potomac rises, because once it has risen then it is no longer possible for Lee to invade the North via the upper Potomac (because there are so many fewer possible crossing points once the river is high, so a couple of brigades would be able to cover them).
Option one involves sending McClellan a lot more troops.
Option two involves spending money and waiting for however long it takes to rebuild the bridges. The bridges still need to be rebuilt, however, and the longer you put it off the later they'll be finished.
Option three involves waiting for an unknown amount of time.
Since option one was not tenable (Halleck wasn't willing to send McClellan enough troops to completely replace 5th and 6th Corps plus a corps for Harpers Ferry, and that number of troops were probably not available to begin with), and option two was not something Halleck was willing to do (he kept delaying starting the work), option three ended up happening by default.
Here's the timeframe:
September 22nd - McClellan wants to rebuild the rail bridge and asks Halleck for the money.
September 23rd - Halleck asks why.
September 24th - McClellan explains he wants to attack Winchester.
September 26th - Halleck denies the funds to repair the bridge, cancels reinforcement, and insists that he wants to agree to whatever McClellan is planning.
September 26th - McClellan explains his plans, mentioning an offensive if the enemy made a mistake (n.b. not protecting Winchester would count as a mistake!)
No reply from Halleck.
October 1st - McClellan makes the point that occupying Harpers Ferry is taken for granted and the bridges are needed anyway.
Halleck replies that he can't authorize the expenditure and the delay from rebuilding the bridges would be unacceptable (a funny thing to say from someone who's spent five days not giving McClellan an answer to his September 26th message).
Lincoln visit goes here.
October 7th - Halleck asks for a plan from McClellan, saying that a plan and agreement to that plan is required before any rebuilding of bridges, railroads etc. is allowed.
McClellan replies the same day or the next with his plans (i.e. cross at Harpers Ferry and push Lee south of Winchester, then switch to a better offensive route).
No reply from Halleck; McClellan's plans have been neither agreed with nor rejected, and he's not been allowed to rebuild the bridges.
October 16th - Lincoln asks why McClellan hasn't advanced yet (message was sent about the 13th and arrived on the 16th, it took several days to reach McClellan). He suggests but does not order a plan of action (the Loudoun Valley movement, basically).
On this date, a recce-in force had happened but no major fighting resulted.
October 17th - McClellan replies that he'd go with Lincoln's plan unless there were reasons not to go for it, and says that as soon as his men had shoes he'd go for it.
October 18th - McClellan asks for the supply problem to be resolved. (Halleck will deny there's a problem.)
October 21st - McClellan writes to Halleck saying that shoes and winter clothing are absolutely essential for the advance.
Halleck's reply is to say his order of the 6th still applies (the one that arrived on the 7th). As a reminder, this is to send his plans and not do anything until they're approved.
October 22nd - McClellan says he'll go with the plan the President wanted.
October 23rd - Halleck approves this plan.
McClellan begins building the pontoon bridge at Berlin MD on the 24th, and has the first troops over the river on the 26th.
So of this period of one month, just about all of it is McClellan waiting for approval from Halleck (where that approval is essential to allow things to start happening). For much of it Halleck isn't saying "no" to McClellan's plan - he's just stalling.