What is the current state of the law on the exclusion of defense evidence?

"While the Constitution . . . prohibits the exclusion of defense evidence under rules that serve no legitimate purpose or that are disproportionate to the ends that they are asserted to promote, well-established rules of evidence permit trial judges to exclude evidence if its probative value is outweighed by certain other factors such as unfair prejudice, confusion of the issues, or potential to mislead the jury." (Holmes v. South Carolina (2006) 547 U.S. 319, 326.)