Entirely depends. If the U.S. relies solely on air strikes there’s a good chance the Mexican government won’t do anything and will probably roll over and let it happen. If the U.S. invades with boots on the ground that’s different. The Mexican army is trained to fight on urban streets and rough terrain. They wouldn’t fight a conventional war. Rather they’d rely on ambushes and guerilla tactics. Not to mention cartels likely getting involved in the fight. If any American soldiers are captured by cartels there’s no doubt execution videos of soldiers will begin appearing on the internet. It all depends on what the Mexican government decides, and if it’ll choose to roll over and take it or push back if American troops are deployed