After Rommel's second defeat of the British in North Africa around Tobruk that city became sieged once again. The first time this happened the Australians defending Tobruk successfully held off the Germans. This time, the city fell after a several week siege. What if Rommel instead of investing Tobruk had pushed the Afrika Korps east after the retreating British and left primarily the Italians to just invest and pin the defenders in Tobruk? Instead of the British getting several weeks of respite to build the el Alamein position they are hounded on their heels by the Germans. I suspect that the British would have proved unable in such conditions to establish a defense at Alamein and in not being able to do so would have lost Egypt.