Lee in Blue: Robert E Fights for The Union?

Having just read "Lee at The Alamo" by everyone's faaaaaavorite Turtledove I am curious at how Lee's actions on the Union side may have impacted the Civil War.

The base premise of course being Lee stays longer as Commander of the Department of Texas and does his duty in defending Federal property in San Antonio against Confederate Texan Militas. We don't really hear how much his stand had on the local German and Mexican populations. Regardless, he eventually turns over things to the Texans and is exchanged along with his men and is regarded a hero by the Union. Recently sworn in Lincoln manages to convince him to fight for the Union in the Missisippi campaign. After that nothing is covered.

So how would things have gone for the Civil War with Lee on hand? I imagine that his loyalty becomes a propaganda victory in itself as he becomes a symbol of loyalty to the Government despite Virginia's secession. It might even galvanize Pro Union elements within the Confederacy.
 
I think the only way Lee would have stayed in the Union is for Virginia to stay in the Union.

Barring that, I don't see him in blue at all.

Now, to go with the OPs question, here's what I think: Lee could probably have beaten any of the commanders the Confederacy would have fielded in 1861. They hadn't discovered Stonewall Jackson or Longstreet yet. And hell, if Virginia had stayed in the Union a bunch of good Confederate generals could have concievably stuck with the Union, so the Confederacy's available pool of good generals would have been much smaller.

With Virginia in the Confederacy and Lee with the Union Army, I bet he would have been treated similarly to George Thomas by his fellow Virginians: poorly.

That's what I think at least.
 
If Virginia stays in the Union (which, barring some huge POD that totally changes Lee's outlook, is the only way you're going to get him in the Union), you're also looking at a much smaller CSA than OTL's. It's very likely that a Union Virginia (or worst case scenario a neutral Virginia) butterflies away the secession of North Carolina, Tennessee, and even Arkansas.

So, smaller CSA, plus an offensive commander like Lee with the resources of the Union at his disposal, means a much shorter ACW.
 
If Virginia doesn't secede then Lee will probably take command of the US Eastern Theater and defeat the South within a year (given the secession butterflies mentioned earlier), perhaps a bit more if Johnston is in command for the CSA. But it is also likely that Lee, like McClellan, would try and minimize damage to Southern property (yes, including slaves), and so like McClellan would not be able to demonstrate his tactical/strategic talents to the full.

No abolition of slavery conceivable: there would be no political/strategic rationale for it, and the risk of having Virginia, Tennessee etc join the Confederacy would be too high. The federal system will remain weak and the issue of whether states can secede unlikely to be fully answered.

If Lee pulls a George H Thomas then he'd be hated all over the South, just like the latter was. He'd still probably be in command in the East and defeat the CSA (probably because his opponent, likely PGT Beauregard, would do something stupid like invade the Union with his rear insecure), perhaps in an even shorter time than had Virginia not seceded.

Still, no abolition of slavery conceivable: a fast victory again removes the political/strategic rationale for abolition. But you would have a stronger federal government and the issue of secession will be answered in full, though still not as fully as OTL.

In either case Lee and his fellow Civil War generals would not be as well-known as they are today. Sad to say it, but their fame did come from the 4 long years of bloodshed.
 
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