https://newrepublic.com/post/180700/trump-incoherent-gettysburg-jokes-twitter
His comments are extremely superficial, but not wrong.
They seem unaware of Pickett’s Charge, ordered by Lee, across a field and up a hill. The Confederacy lost lost about an eighth of all their casualties in that three day battle during that less than one-hour charge.
“They seem unaware of Pickett’s Charge, “
I believe the hill is Seminary Ridge. The charge was generally on flat ground until the last few hundred yards, close to the ridge. There is nothing illogical or unreasonable about saying “don’t fight uphill”, although in many cases like Iwo Jima you are attacking enemy who has the high ground.