Three P-38 fighter groups were operational in the Pacific, where Lightnings were accredited with the destruction of more Japanese aircraft than any other fighter in USSAF service. They are well recorded in the air force's history for a string of memorable actions, including the interception and destruction, some 550 miles (885 km) from their base, at Guadalcanal, of the Mitsubishi G4M carrying Japan's Admiral Isoroku Yamamoto, a skilful action carried out by aircraft from the 70th, 112th and 339th Fighter Squadrons. And, of course, the USAAF's 'ace of aces' of World War II, Major Richard I. Bong, scored all of his 40 confirmed victories while flying P-38s in the Pacific theatre. In Europe P-38s served mainly with the 9th Air Force, used extensively on long-range fighter escort duties in support of 8th Air Force daylight bombing missions against German targets.
It was the return bomber escort trips of those Lightnings the Germans didn't care for at all.
I always found the P38's use in the ETO to be a curious contradiction. One one hand you have the so-so performance of the aircraft in the bomber escort role. OTOH, the Germans seemed to fear this aircraft more than any other in service (save perhaps the Spit).
Trying to put myself into the position of a Luftwaffe pilot attempting to attack a bomber formation I can only conclude that with Lightnings defending you only get 1 pass. Once the P38 engages, you have one alternative -- point your nose at the deck & dive away as steeply as you dare. The P38 was restricted in a dive because of control compressibility. It lost elevator function & couldn't pull out.
You wouldn't want to get into a turning fight with a Lightning because they had a pretty darn good turn rate. Good in the climb as well. And if the Lightning 'touched' your Me-109 with it's impressive firepower, well, game over. That leaves the German with one sure option: dive for your life.