Here's what the Supreme Court said in 1951 in Hoffman v. United States, 341 U.S. 479, 485-87:
The Fifth Amendment declares in part that ‘No person * * * shall be compelled in any Criminal Case to be a witness *486 against himself’. This guarantee against testimonial compulsion, like other provisions of the Bill of Rights, ‘was added to the original Constitution in the conviction that too high a price may be paid even for the unhampered enforcement of the criminal law and that, in its attainment, other social objects of a free society should not be sacrificed.’ Feldman v. United States, 1944, 322 U.S. 487, 489, 64 S.Ct. 1082, 1083, 88 L.Ed. 1408. This provision of the Amendment must be accorded liberal construction in favor of the right it was intended to secure. Counselman v. Hitchcock, 1892, 142 U.S. 547, 562, 12 S.Ct. 195, 197, 35 L.Ed. 1110; Arndstein v. McCarthy, 1920, 254 U.S. 71, 72—73, 41 S.Ct. 26, 65 L.Ed. 138.
The privilege afforded not only extends to answers that would in themselves support a conviction under a federal criminal statute but likewise embraces those which would furnish a link in the chain of evidence needed to prosecute the claimant for a federal crime. (Patricia) Blau v. United States, 1950, 340 U.S. 159, 71 S.Ct. 223. But this protection must be confined to instances where the witness has reasonable cause to apprehend danger from a direct answer. Mason v. United States, 1917, 244 U.S. 362, 365, 37 S.Ct. 621, 622, 61 L.Ed. 1198, and cases cited. The witness is not exonerated from answering merely because he declares that in so doing he would incriminate himself—his say-so does not of itself establish the hazard of incrimination. It is for the court to say whether his silence is justified, Rogers v. United States, 1951, 340 U.S. 367, 71 S.Ct. 438, and to require him to answer if ‘it clearly appears to the court that he is mistaken.’ Temple v. Commonwealth, 1880, 75 Va. 892, 899. However, if the witness, upon interposing his claim, were required to prove the hazard in the sense in which a claim is usually required to be established in court, he would be compelled to surrender the very protection which the privilege is designed to guarantee. To sustain the privilege, it need only be evident from the implications of the question, in the setting in which it is asked, *487 that a responsive answer to the question or an explanation of why it cannot be answered might be dangerous because injurious disclosure could result. The trial judge in appraising the claim ‘must be governed as much by his personal perception of the peculiarities of the case as by the facts actually in evidence.’ See Taft, J., in Ex parte Irvine, C.C.S.D.Ohio, 1896, 74 F. 954, 960.
The witness must have reasonable cause to believe that his answer will incriminate him or reasonable cause to believe that his answer will provide a link to evidence that will incriminate him. In other words, Donald Trump has to have reasonable cause to believe he can directly or indirectly incriminate himself by answering questions.
