The federal government, through the use of its budgetary powers over highway funding, issues rules that will withhold such funding unless states comply with new guidelines making the minimum drinking age for use of alcoholic products to be 21 years old. A number of states, such as Colorado, had an 18-year drinking age for low alcohol (3.2) beer. Colorado was threatened with loss of federal highway funds if it did not change that law to the federally recommended national standard of 21 years old for all alcoholic products. Is this constitutional?