I like a "biopic" about Grant: Start with Lee's surrender, then flash back to his boyhood, time at West Point, and all of his failures. Many scenes come to mind: his horsemanship at West Point, marriage to the daughter of a rich slave owner, failure at farming, working moving tanned hides for his father, waiting outside of McClellan's tent, saying "we'll get 'em tomorrow" after the first day of Shiloh, the many failures at Vicksburg before the siege, etc. etc. His life is a series of dramatic scenes.
Or you could start with him writing his autobiography as he was succumbing to cancer, with the entire movie a flashback. I would gloss over his presidency
I like the idea of a Grant biopic too (and I believe there is one in the making by Appian Way.) The challenge is to find the best focal point.
Grant and Sherman would be one way to go. Both looking in from the outside at the beginning of the War - when Sherman was "crazy" and Grant was "drunk." Sherman, long out of the army, gets a commission through his family connections but is soon believed to be out of his mind because he quickly comes to the absurd conclusion that hundreds of thousands of troops will be needed to put down the rebellion. Sherman knows Southerners, spent the last year before the war teaching at a military academy in Louisiana, but no one is listening. Grant, also years away from his army days, cooling his heels outside McLellan's headquarters, patient, perhaps aware that McLellan is keeping alive the old stories about that time on the Oregon Coast. McLellan doesn't even give him the time of day.
They've met before at West Point. Grant remembers the outgoing redhead a couple of years ahead of him who riffed on the initials "U S" and settled on the name "Sam Grant." Sherman remembers the shy younger boy, still not fully grown, the horse whisperer.
Separately they make their way through the ranks, Sherman begging Lincoln not to put him in charge of anything, Grant taking any opportunity he gets in between the many changes in command in the West to actually attack something.
Shiloh is their trial by fire and where they bond. Both have a lot to prove. After the first day's battle Sherman approaches Grant, who is standing under a tree all night because he can't sleep and has to listen to the cries of the dying and wounded. Sherman is about to mention retreat, but something about Grant stops him, so he just says "We've had the devil's own day." "Lick 'em tomorrow," is Grant's reply.
After that they are besties. What do they talk about in their tents and how do they bond? Sherman talks Grant out of resigning from the army after Shiloh. Other officers observe a reunion between them with great relish - like two schoolboys getting together.
Arguing over the approach to Vicksburg, but amicably. Sherman wants to retreat and regroup, Grant wants to press on. When Grant's star rises, does Sherman have any regrets about asking to always be second in command? How does he feel about Grant's move east?
Then Sherman's own meteoric rise as he takes Atlanta and Savannah. A meeting on the River Queen with Lincoln, so different now.
Sherman's humiliation when his surrender terms with Johnston are rejected and Grant takes on the job of breaking it to him, but the situation is inflamed by Stanton going to the press and accusing Sherman of treason.
Sherman begging Grant not to go into politics. It won't suit him. He knows his friend. A growing apart during Grant's presidency over many issues.
While Grant is dying Sherman leads an initiative to get Congress to restore his army pension, which he lost when he took the presidency, so that his widow Julia will not be destitute.
A last sad meeting between the two men shortly before Grant's death.