The USA can bomb them for years but that isn't actually going to take land. You need boots on the ground to conquer land. Unfortunately the US is outnumbered over 20 - 1 and can't get replacements. The gap between modern jets and 1940's aircraft is much wider then the gap between modern infantry and Nazi infantry.

Outnumbered 20 to 1 isn't as big of an issue as you think - during WW2, over 2.8 million Germans surrendered to the Western allies by April of 1945. In the same time, the Western allies took 250,000 killed or captured as prisoners - a great ratio for the Allies of 1945 to whom the Germans were willing to surrender. The Germans would be even more eager to surrender to a force as overwhelming as the military today.

The modern US military would easily take on 20 to 1 odds with the Germans - German tanks would have zero chance of taking out an Abrams (even getting in range would be difficult) nor would German artillery have any chance of stopping our mobile self-propelled artillery and MLRS (multiple-launch rocket systems) from stopping their artillery positions. Infantry would only be needed to hold the ground and to support the main armored thrust, for which the Germans even with 10,000+ tanks would struggle against 2,000 Abrams.

Attack helicopters and aerial gunships like the AC-130 further tilt the battle vastly in favor of the US. These are all weapons that are called force multipliers for a reason: they make individual units much greater than the sum of its parts.

20 to 1 odds don't matter if you're so thoroughly outgunned and being destroyed with impunity: you would surrender or desert instead of standing and being annihilating.

And speaking of which, the US wouldn't need to bomb the Axis for a decade. Individual fighters and bombers can strike at the industry of the Axis with impunity + airbases + railways and other logistical centers would further impede any hope of the Axis mounting a coordinated defense.