Relevant and probative evidence may be excluded as "unduly prejudicial" -- to prevent undue prejudice because of emotion, to prevent waste of time, and to prevent other such harms -- only if the risk of such harms substantially outweighs the probative value of the offered evidence.

Sandstrom v. Montana, 442 U.S. 510, pin? (1979).The law is disordered on the question of when a presumption in a criminal trial violates the constitutionally-mandated standard of proof beyond a reasonable doubt.

Cf. Arizona v. Fulminate, 499 U.S. 279, 295 (1991) (plurality of four Justices: "The search for truth is indeed central to our system of justice, but 'certain constitutional rights are not, and should not be, subject to harmless-error analysis because those rights protect important values that...The determination of facts and the accurate determination of facts are important purposes of the process of proof and the law of evidence in America.

United States v. Adams, 401 F.3d 886, 899 (8th Cir. 2005) (upholding trial court's admission into evidence (1) of accused Parker's prior drug convictions, and (2) of accused Adams' participation in the Serrano conspiracy, where both accused conceded the relevancy of the evidence to prove knowledge and...Evidence of a criminal or wrongful act apart from the act that at issue at trial Is not barred by the prohibition against circumstantial use of character if intent, knowledge, mistake, or accident is a legally-material factual issue, the opposing party suggests the non-existence of knowledge or urges mistake or accident as a defense, and evidence of another crime, wrong, or act is offered to prove the knowledge or the absence of mistake or accident by a criminal defendant or other person.