In Blair v. United States (1918), the Supreme Court ruled that a grand jury witness could not refuse to answer questions on the grounds that they might incriminate him in future criminal proceedings, thus upholding the concept of compulsory self-incrimination. The case arose when William A. Blair was subpoenaed by a federal grand jury investigating potential violations of banking laws and refused to answer certain questions, arguing it would expose him to possible prosecution for unrelated offenses. In its decision, the court held that since there were no charges pending against Blair at the time he testified before the grand jury, his fear of future prosecution was merely speculative and did not justify his refusal to testify.

In the dissenting opinion for Blair v. United States, Justice McReynolds argued that the majority's decision violated a fundamental principle of American law: no individual should be compelled to provide evidence against themselves. He contended that forcing an individual to appear before a grand jury and answer questions about their own potential criminal conduct was inherently coercive and thus unconstitutional under the Fifth Amendment. Furthermore, he disagreed with the majority's assertion that granting immunity from prosecution sufficiently protected individuals' rights; in his view, this did not eliminate the risk of self-incrimination because any information revealed could still potentially be used against them in other ways. Finally, he expressed concern over potential abuses of power by prosecutors who might use grand juries as tools for harassment or intimidation rather than genuine fact-finding bodies.