In WW2 did America ever fight Germany when they were at their peak militarily? Or when they arrived in Europe they faced a weakened and worn out Germany? (I know they were losing at that point) or if there were any battles US lost in Europe to them.
For example Russia is defeated or instead for whatever reason they don't fight Russia and instead get a lend lease type of assistance from them (But no military assistance) how do America/Allies fair against Germany in Europe? Or would it be impossible for them to land in Europe?
No, not really. The one time where Germany was anywhere close to their 'prime' in terms of military skill/manpower/relative combat power was early in the Tunisian campaign, but even by that point the 10th Panzer division was still recovering from Eastern Front, the HG division was still forming, and Rommel's troops had been worn down in Egypt and were a shell of their former selves. Plus then the logistics, numbers, and supporting firepower was heavily on the side of the Allies by late 1942. From then on the Americans always fought at a major advantage over the Germans, even in Sicily and at Salerno when things got hairy. By Normandy the Germans were a shell, even if they did have some quality units, but none were up to ration strength and in terms of facing Allied air power and naval fire support the Germans couldn't even fight as cohesive divisions for fear of being smashed if they tried to attack.
The Soviets bore the brunt of peak German strength and wore it down over years only thanks to their virtually unlimited strategic depth, Lend-Lease, and huge pools of manpower. Had they been the size of Western Europe only they would have been defeated before they could learn the harsh lessons of modern combat. It cost them dearly, with probably around 30 million dead, by some estimates 14-15 million of those were soldiers or combatants out of uniform.
https://en.wikipedia.org/wiki/World...viet_Union#Russian_Military_Archives_database
That's not even counting wounded.
The UK too faced the Germans at their peak and were smashed repeatedly, starting in 1940 and running right until the Germans ran out of logistic support in Egypt in July 1942. They couldn't win until they built up a huge superiority in supply, air power, firepower, and manpower while sitting deep in their colonial territory, while Rommel was at the very end of his and worn down by lack of supply and replacements; then the US showed up in that situation and the Germans had to toss in barely adequate blocking detachments on the fly in November 1942. The US got all the benefit of the dying the Brits and Soviets had done to that point. Even in the air during the strategic bombing campaign the USAAF didn't really make a significant impact until 1943 when they started bombing Germany and that was past the prime of the Luftwaffe thanks to losses in the BoB and on the Eastern Front to that point. From them on the USAAF did the majority of Luftwaffe killing, but they had a well softened up target by then, aided by incompetent Nazi administrators (Udet, Goering, etc).
Eventually yes, it doesn't matter how many tanks you can now put into France if it just means more targets for the RAF and USAAF. It will take longer but ultimately the strategy will be the same as OTL, achieve air supremacy over France, bombard the German army and their infrastructure, invade. The bomb might be ready prior to ITTL's Overlord being ready to go which could later create allusions to the Hiroshima debate. Was it better to destroy Hamburg and Nuremburg than avoid the casualties of invading France?
It is a bit tougher to say if there never was an Eastern Front. The entire war would have changed and the US might never get involved. With Germany getting LL from the USSR and can structure their construction priorities to the needs of fighting the UK, both naval and air production would be a lot higher from 1940 on, as there is no preparation for Barbarossa, which sucked up a huge part of German resources post-BoB, plus there is no need for slave labor if they can demobilize their skilled labor from army service and have all the raw materials they don't need to produce themselves to build weapons. Britain probably is defeated then before the US can enter the war or at least make a major impact. The entire scope of the Mediterranean campaign changes without Barbarossa being planned or prepared for.
Now if Barbarossa happens and succeeds due to wild luck say with Stalin dying and the USSR falling apart in a power struggle to replace him, then things get interesting, because the Germans could secure Soviet resources, but need at least 2 million men to garrison/exploit the East, plus rebuild what was damaged in the war, maintain supply lines, enforce their slave labor policies, and probably fight the remnants of Soviet military units; it's been discussed before, but the Soviet partisan movement could not exist without support from Moscow and it was Moscow that fostered it from 1942 on with constant supply drops, parachuting in trained personnel, evacuating wounded, coordinating actions and groups, etc. Then the Germans can afford to demobilize probably 50 divisions to return labor to factories and the Luftwaffe/navy (that was the plan), shift build priorities, fight in the Medditerranean differently, husband their air strength (no pillaging instructors from flight schools to supply cut off units in the winter campaigns), plus have enough fuel not being use in the East or even by having captured oil fields to exploit to keep up the pilot training program and expand it. Then things are a bit different, because Rommel can be properly supported with all the things he asked for IOTL and never got and Malta taken down in early 1942 with effectively unlimited Luftwaffe commitments to cut off supply.
Then things largely come down to what happens in North Africa (if Egypt falls then it's likely the US panics and puts Operation Torch troops into the Middle East and may well even try and rush an invasion of France which will not go well in late 1942 with no Eastern Front; as it was by late 1942 the 8th Air Force had less than 300 bombers and had only started combat operations in August). The strategic air war kicks up and the Allies have to build up a much larger army, which is possible thanks to no LL to Russia, which could have equipped 60 additional US divisions. If the Allies don't rush into France they wait on the Mediterranean strategy and strategic air war, but without the expense of the East and instead access to those resources the Germans are a far different threat than IOTL. The war in Europe will be long and a LOT bloodier for the Wallies than IOTL. Operation Vegetarian might even happen. The air war isn't likely to be won by 1944 ITTL.