If you listened to yesterday's arguments in the litigation attempting to remove Donald Trump from the ballot in Colorado, you would hear a brief cameo from issue preclusion.
Colorado made a legal determination (about the scope of § 3) and factual finding (Trump engaged in insurrection), in an action to which Trump was a party (remember he intervened). Those legal and factual conclusions may have preclusive effect in proceedings to exclude him in other states. The issue was litigated and resolved, it was necessary to the judgment, and Trump had a full-and-fair opportunity to litigate it. Some Justices raised the concern that this would allow one state court--the first one to address the issue--to exclude a candidate from the ballot in all states. Remember that preclusion applies between states and between states and federal.
Trump's attorney identified an out, at least in this case: Colorado does not recognize non-mutual preclusion. Since any new state is a different party from Trump, preclusion would not apply. And Court # 2 applies the preclusion rules from Court # 1--giving the prior decision the same preclusive effect the issuing court would have given its decision. So Colorado's determination that Trump engaged in insurrection would not bind, say, an Illinois court considering whether to exclude Trump from its ballot.
The Court seems likely to say states cannot keep candidates off ballots for federal office, so this is moot. But see it as a surrounding issue.
Civ Pro really is all around us.
