The Mexican government requires that tourists get auto liability insurance from a Mexico-based insurance company. Although your USAA auto policy may provide limited coverage for any loss or damage that occurs within a certain distance from the U.S.-Mexico border (check your policy for details), it doesn't provide the insurance legally required for travel in Mexico.
Please note that this website provides only a summary of auto insurance, written to illustrate in general terms how auto insurance works. Your insurance policy is the legal contract that contains the terms and limitations of your coverage. You should carefully review the contents of your policy. All products and coverages are subject to availability and limitations. Whether an accident or other loss is covered is subject to the terms and conditions of your insurance policy.