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  1. Most major rules are not challenged in court. To be exact, only 21.2% of the major rules in our dataset ended up in court, meaning the vast majority of major rules go unchallenged. But the challenge rate has risen over time. As a result, federal courts are resolving many more challenges to major rules than they once did.
  2. Some agencies’ major rules landed in court more frequently than others. The 76.2% challenge rate for the Environmental Protection Agency (EPA) was a notable outlier.
  3. Our study finds lower overall agency win rates than most other studies. Previous studies typically found agency win rates of around 60–70%, with most studies closer to the top of that range. In contrast, our study finds an overall agency win rate of 49.1% (by major rules) and 56.1% (by controlling opinions). This discrepancy likely stems from multiple factors.  We grouped mixed results with losses in the calculation of our overall win rate (we also present such mixed results side-by-side with outright wins and losses for context). Other studies also covered earlier timespans; for example, none included the Trump Administration. Given our study’s consistent unit of analysis and timespan, it is likely that declining agency win rates over time (and, relatedly, the sharp decline during the Trump Administration) at least partly explains why we found lower overall agency win rates than earlier studies. Readers should keep these nuances in mind.  
  4. The two-term presidents in our study (Clinton, W. Bush, and Obama) had higher win rates for major rules issued in their second term. Our study does not reveal the cause of such fluctuations, but they should be kept in mind when comparing agency win rates across administrations and when analyzing data from studies that captured opinions addressing agency actions from a particular presidential term.
  5. Win rates varied widely across agencies. Among the top 10 rule-issuing agencies, the Federal Communications Commission (FCC) had the highest win rate at 73.9%. EPA and the Securities and Exchange Commission (SEC) had the lowest win rates at 36.4% and 38.5%, respectively. But EPA also had the highest rate of mixed results. Weighing those mixed results changes the picture for EPA, especially if one includes mixed results that led only to a remand without vacatur. Taking that approach, EPA’s win rate rises to 62.1%.
  6. Our study finds that independent agencies (as defined under 44 U.S.C. § 3502) had higher win rates than executive agencies (57.4% versus 47.3%). Agencies led by multimember commissions similarly had higher win rates than single-headed agencies (59.0% versus 47.2%).
  7. While around half of all challenges to major rules were filed in either the U.S. District Court for the District of Columbia or the U.S. Court of Appeals for the D.C. Circuit, these two courts’ preeminence declined over time. The D.C. Circuit’s decline was starkest, dropping from 53.2% for challenges to the Clinton Administration’s major rules to 38.1% (W. Bush), 27.7% (Obama), and 11.7% (Trump).
  8. Partisan trends in our study paint a mixed picture. Republican administrations generally fared better in front of judges appointed by Republican presidents and vice versa, but Democratic administrations fared considerably better in front of mixed panel majorities than Republican administrations (73.8% versus 45.7%).
  9. Chevron citations in controlling opinions addressing challenges to major rules arguably follow Chevron’s own arc: They rise from Carter appointees (47.1%) through Reagan (60.4%) and H.W. Bush appointees (65.2%), before declining through Clinton (54.9%), W. Bush (49.2%), Obama (46.8%), and Trump (28.0%) appointees.
  10. The Biden Administration continues to issue major rules, and many challenges to its existing rules remain pending. Comparisons to previous administrations could thus be misleading. But our analysis of the datapoints through early December 2023 finds that the challenge rate to the Biden Administration’s major rules (20.1%) is more in line with earlier administrations than the Trump Administration. Its win rate falls somewhere in between: 40.7% by major rules and 47.9% by controlling opinions. This preliminary data suggests that, although the Trump Administration may have had an unusually low win rate, it may have been a dip in a longer downward trend.