Explain this to me.
Battle of the Bulge. The US has been fighting the Germans for years. The Axis launch a surprise attack against either understrength or, in the case of the Golden Lions, utterly inexperienced US units. They make good progress, it is the only time in the war that a US division is destroyed, but eventually are ground to a halt and by the end of it, the plan to loop North to encircle the British at the coast failed, the Germans are moved back to their start lines, the battlefield in US hands. Considered a great US victory.
Kasserine Pass, The US hasn't really had much experience fighting Germans The Axis launch a surprise attack against inexperienced US units. They make good initial progress, surround and effectively destroy two infantry regiments, are held up for two assaults until finally the Italians break the American line on the third try. They are finally held at the next defensive line, and at the end of it all, the plan to loop North and encircle the British at the coast failed. The Germans are moved back to their start lines, the battlefield in US hands. Considered a great US disaster.
Outside of the fact that at the time, the US weren't accustomed to the idea that they might not walk over the Axis, so the idea that the Germans weren't a pushover was a novelty, why with the benefits of 75 years of hindsight are there such differing views?
Kasserine Pass was a German victory. It achieved its limited aims, although not as much as was hoped for. It was an operation-level spoiling attack, a limited attack intended to hurt US preparations for attacking the Germans. Part of this larger goal was the target of capturing US supply bases, to (a) deny those supplies to the US, and (b) to capture those supplies for German use; this was not achieved.
The Germans, with overall numerical inferiority, and at a great disadvantage in terms of artillery, launched a frontal attack on defended passes, achieving a breakthrough at Kasserine Pass. Their exploitation of this breakthrough ground to halt due to limited supplies and overwhelming Allied artillery superiority. Content with having achieved their goal of slowing US preparation for attack, and inflicting disproportionate casualties (about 7 times greater!), Rommel halted the attack while he was ahead.
While the US forces were not expecting such aggressive behaviour from the Germans, this was not a surprise attack on a quiet front like the Ardennes Offensive was. It succeeded as well as it did because US forces were mismanaged in the battle - officers were relieved of their commands for good reasons.
Verdict: Kasserine Pass was a minor but significant German victory.
The Ardennes Offensive did not achieve its operational or strategic goals. The strategic goals - to capture Antwerp, and force a separate peace with the Western Allies - were ridiculously unrealistic. The first part of this, Antwerp, was in principle feasible, if sufficient resources (troops and supplies) were available. The second part was not realistic. The offensive could never be a strategic victory for Germany.
Operationally, the schedule was ambitious - the only feasible way to reach the objectives on-time would be for US resistance to completely collapse after the front line had been broken. This was a serious problem - it was not just a matter of objectives being reached late, but it would reduce the chance of taking those objectives in the first place. If the planned speed could not be maintained, the Allies would have more time to strengthen their defences, more fighting would reduce German supplies, and give more time for the weather to clear, allowing overwhelming Allied air superiority to fall upon the Germans. For example, it was hoped that Bastogne would be taken on the first day, or at the latest, early on the 2nd day (i.e., 17th December). German forces only reached Bastogne on the 19th, and US 101st Airborne Division had arrived earlier that morning, and the Germans could not take Bastogne. St Vith was a 2nd day objective, was reached on the 3rd day, and taken on the 6th day. The German generals knew the problems with the ambitious objectives and timetable: as von Rundstedt said, "If we had reached the Meuse, we should have got down on our knees and thanked God - let alone tried to reach Antwerp".
If the strategic objectives of the offensive were impossible to achieve, and the operational objectives could, realistically, only be partially-achieved, and behind schedule, the offensive could never be the great victory Hitler was hoping for. Could the Germans achieve anything useful? If they could inflict disproportionate casualties, as they had done at Kasserine Pass, perhaps a limited victory of a kind could be achieved. In the end, the Germans suffered greater losses. Both sides lost a similar number of men, with the Germans losing more. German losses in tanks and aircraft were much greater (tank losses are often much greater for a retreating force, since tanks lost to mechanical breakdown and lack of fuel become permanent losses). The end result was a front line approximately where it had started, and a victory for the Allies in terms of attrition.
The Bulge was a US failure in terms of intelligence and preparedness. Germany managed to maintain surprise while gathering a powerful force of the best German units available, allowing an attack with a numerical superiority of more than 2 to 1, with plentiful artillery support. The green US 99th and 106th infantry divisions were defending frontages over four times greater than US doctrine said they should. The loss of two regiments of the 106th is hardly unexpected considering the German strength that fell on them. The stubborn defence of Elsenborn Ridge by the 99th, and of St Vith by the surviving regiment of the 106th was superb; the US failure at Kasserine is all the worse when compared with these defensive battles.
In summary,
Kasserine Pass was a German victory because they achieved enough of their limited objectives, and inflicted very disproportionate casualties on the US forces. US failures were at the level of command on the battlefield.
The Battle of the Bulge was an Allied victory because the Germans failed to achieve their strategic and operational objectives, and suffered greater casualties at a time when they couldn't even afford equal casualties. US failures were at the strategic level, and of intelligence. US forces performed well on the battlefield, including against great odds on many occasions.
The US intelligence failure leading up the Bulge is forgivable enough - the German plan was, in many ways, a stupid plan. Who expects a stupid plan from a skilled enemy? There was no sensible strategic reason for the attack (as noted above, the strategic goals were impossible to achieve), so there was no strategic reason to expect such an attack.
The German plan was perhaps not so stupid. Conservative game theory states that a rational enemy would not make such an attack, since the risks overwhelmingly outweigh the expected gains. On the other hand, it is not so unexpected from behavioral game theory. A risky strategy, with the expected losses outweighing the expected gains, can be a better choice than the conservative strategy - the slim chance of victory it offers can be greater than the zero chance of victory from following the conservative strategy. Is it such a terrible thing to lose faster if the risky strategy fails?