Checked Luggage - International to Domestic

I will be traveling MGA-IAH-BWI in April, all on United metal on a single ticket. If I check a bag in MGA, will I have to collect it and clear customs at IAH and then re-check, or will it get transferred to the domestic flight without a customs inspection?

Thanks! I have a relatively tight connection if the former, which will dictate how I pack (checked vs carry-on).