The trust responsibility is a legal doctrine that has grown out of treaties, statutes, court decisions, and other dealings between the United States and Indian tribes. The U.S. is the trustee, and the tribes are similar to beneficiaries.
Under this trust responsibility, the U.S. has a legal obligation to protect tribes' assets and provide needed services to Indian people. This prevents the U.S. from applying means tests to the funds it appropriates for Indian tribes and Indian people.
Trust obligations are legally binding.
The U.S. is obligated to provide certain services to Indian tribes and Indian people because of treaties signed by the U.S. and tribes, statutes passed by the U.S. Congress, and Supreme Court decisions. Trust obligations, as defined by federal law, include the provision of health, education and other services to Indian people.
The trust relationship was based on the notion of Indian sovereignty.
Between 1787 and 1871, the U.S. and Indian tribes signed hundreds of treaties. In nearly every one of these treaties, tribes gave up lands in return for goods, money and other resources that were promised by the U.S. government. When the U.S. took Indian land and Indian resources, it made binding legal agreements that tribes would exercise sovereign authority within their reservation boundaries and be funded into perpetuity by the federal government.
Trust obligations are based on need so funds can not be means-tested.
Federal funds are appropriated for Indian tribes and Indian people because the U.S. has a legal obligation to do so. Dependency and need are not the basis for providing these funds although most tribes have critical unmet needs. Therefore, it is inappropriate to require means-testing for any of these funds. For a useful comparison, think of trust obligations as contractual agreements not welfare programs.