Evidence from the aftermath of the November 2020 U.S. election indicates that the low‑probability scenario Sacks described did in fact occur in substance:

1. Serious attempt to overturn a certified election result
   After Election Day, Donald Trump and allies launched an extensive campaign to overturn the outcome, including more than 60 lawsuits (all unsuccessful), pressure on state officials to change results, and a coordinated fake‑elector scheme, all aimed at preventing Joe Biden’s lawful victory from taking effect. (en.wikipedia.org)

2. January 6 and pressure on Congress/Vice President
   These efforts culminated in the January 6, 2021 attack on the U.S. Capitol, explicitly intended to disrupt and delay the Electoral College count and pressure Congress and Vice President Pence to overturn the result. (en.wikipedia.org) This went beyond Bush v. Gore–style litigation into violence and an attempted subversion of constitutional procedures.

3. Ongoing legitimacy crisis around elections
   The false "stolen election" narrative (“Big Lie”) became the basis of a broad election‑denial movement that continues to claim U.S. elections are rigged despite lack of evidence, eroding confidence in electoral integrity. (en.wikipedia.org) Congressional testimony and polling summarized in the January 6 investigation record show that majorities of Americans by early 2022 believed U.S. democracy was “in crisis and at risk of failing” and had low confidence in honest elections—clear indicators of a legitimacy crisis. (govinfo.gov)

4. Serious political damage at home and abroad
   The Capitol attack and subsequent denialism were widely described as a grave attack on democracy, including by foreign leaders who said that armed supporters of an outgoing president undermined the principle of legitimate elections. (en.wikipedia.org)

While some officials argue the U.S. ultimately avoided a full‐blown constitutional breakdown, the combination of an attempted overturning of the election, the Jan 6 insurrection, and a persistent crisis of electoral legitimacy matches—and arguably exceeds—the "constitutional or legitimacy crisis" scenario Sacks outlined. Therefore the prediction is best scored as right.