Most historians feel it would have taken a year to mount another assault, but we would still have won (In hindsight, we did beat the Germans to the A-Bomb which was our Ace in the hole). You have to consider that by mid-1944 the best German fighting divisions had been bled-out in fierce fighting in North Africa, up through Italy and all along the Russian front (Where a majority of their divisions were tied-up). At Omaha Beach the German Division defending it was battle-tested but also decimated. They had been sent there for R&R, retraining and to re-equip after being ripped on the Russian Front. There were a lot of conscripted Poles defending that beachhead too, from construction battalions.
D-Day was a brilliant maneuver - first making the Germans think they were going to invade Calls to the North, then catching them during bad weather when they didn't expect it and Western Defenses commander, Erwin Rommel had left for home for a furlough. The fight for the beach was vicious and the Germans then through everything they had during the subsequent Hedgerow fighting to slow them down. I had the good fortune to interview a number of those who were there including a couple of Germans, they had a very interesting perspective. But people sometimes forget there was a lot of war fought before D-Day by hundreds of thousands of other brave Americans (Brits and Russians) which removed dozens of their very best divisions like SS Panzer and Parachute outfits from the battlefield. Guys in the first wave told me when they took the beach there were thousands of 8mm wooden training bullets washed up on the tide the Germans used because they ran out of regular ammunition in the bunkers and couldn't get resupplied.
