I should have used these examples in our class discussion of preclusion. But putting them here hopefully can help a bit in understanding issue preclusion and in understanding current events.
1) Carroll v. Trump. Trump testified on Thursday in the defamation lawsuit by journalist E. Jean Carroll, alleging that Trump sexually assaulted her many years ago and defamed her by falsely denying the assault. But his testimony lasted only a few minutes and a few questions. Issue preclusion explains this.
Carroll brought two defamation actions against Trump. Case II (the current trial) arose from statements Trump made while President; Case I arose from statements Trump made after leaving office. Case I went to trial last year and a jury found in favor of Carroll and awarded her $ 5 million in damages. In reaching that verdict, the jury found that Trump had sexually abused her via various acts.
The judge in Case II found that the Case I verdict had issue-preclusive effect. Trump could not contest that he had, in fact, sexually abused Carroll, which meant he could not contest the falsity of his second round of (post-presidency) statements denying the abuse. The trial in Case II thus is limited to damages; liability for defamation is established by the prior factual conclusions. And that explains why Trump's testimony was so limited. Testimony denying the truth of Carroll's sexual-abuse allegations is irrelevant, because the fact was established.
Note, by the way, that although the parties are the same in both cases, this is issue preclusion, not claim preclusion. Each defamatory act constitutes a distinct claim for defamation. This is issue preclusion. A factual issue--did Trump sexually abuse Carroll--was established in Case I. And the distinct claims in Case II must be litigated in light of that finding.
2) Trump Eligibility. This is forward-looking, something to keep an eye on, depending on what SCOTUS does with the Colorado case. If the Court affirms the Colorado Supreme Court on the conclusion that Trump engaged in or supported insurrection and is ineligible to be president, that is a factual question that would have preclusive effect on other, discrete actions challenging Trump's eligibility in other states. In other words, a challenge to Trump's eligibility in, e.g., Wisconsin, constitutes a new civil action. But the conclusion that he engaged in or supported insurrection would preclude Trump from arguing otherwise in the Wisconsin action and would require the Wisconsin court to find he did engage and decide that case accordingly.
The Trump/ballot cases also offer a good example of the limitations of what a court, including SCOTUS, does in deciding any one case. The question before the Court is Trump's eligibility in Colorado; that turns on a bunch of federal legal issues (the scope of § 3 of the 14th Amendment, whether the President is an officer of the United States, whether January 6 qualifies as an insurrection, etc.). SCOTUS's resolution of those issues immediately resolves only the Colorado case. It also establishes legal principles that guide similar future cases. But those future cases must be brought and litigated. So if SCOTUS affirms the Colorado Supreme Court, the only immediate effect is that Trump cannot be on the ballot in Colorado. It will take 50 more lawsuits to have him ineligible in other jurisdictions. Those courts must follow what SCOTUS says (whether as a matter of precedent or preclusion). But those future cases are necessary.
