Key facts about RFK Jr. and the 2024 Democratic primaries:

• Robert F. Kennedy Jr. launched a 2024 presidential bid as a Democrat in April 2023, then left the Democratic Party and announced an independent run on October 9, 2023, declaring his “independence from the Democratic party.” (en.wikipedia.org)
• While a Democratic candidate, RFK Jr. did attract notable grassroots interest, polling around 19–25% among Democratic primary voters, with Biden still clearly ahead (roughly 57–60%). (pjmedia.com) That’s meaningful support but not a frontrunner “wave” on track to win the nomination.
• RFK Jr. repeatedly accused the DNC of “rigging” the primary via rules changes: no sanctioned primary debates and a reordered calendar that favored Biden (e.g., elevating South Carolina), and he argued that the superdelegate math meant he would need to win an overwhelming share of states to beat Biden. (breitbart.com) He cited these barriers while signaling he might seek “other alternatives,” which he then did by running as an independent.
• Because RFK Jr. exited the Democratic primaries before any voting, there was never a situation where an anti‑establishment Democrat was actually winning primaries and delegates and then blocked at the convention via superdelegates or similar formal mechanisms. The 2024 Democratic primaries themselves were effectively a low‑contest incumbent race that Biden dominated. (en.wikipedia.org)
• After Biden later dropped out in 2024, party leaders changed convention rules so superdelegates could vote on the first ballot in a virtual roll call that nominated Kamala Harris, underscoring the establishment’s willingness to use rule changes and superdelegates to shape outcomes. (en.wikipedia.org) But this move was about replacing a faltering incumbent with his vice president, not about stopping a surging anti‑establishment insurgent.
• Outside the primary context, the Democratic Party and Democratic‑aligned actors did pursue legal and procedural efforts that hindered RFK Jr.’s independent candidacy (e.g., an FEC complaint over alleged illegal coordination with a super PAC, and ballot‑access fights like those in Nevada), but those are not the exact superdelegate/primary‑process scenario the prediction described. (theguardian.com)

Taken together, the condition in Sacks’s prediction—an anti‑establishment Democrat building a sufficiently strong grassroots wave inside the Democratic primaries to plausibly win—never fully materialized. RFK Jr. had meaningful but minority support and left the party before any test of convention‑level intervention, and no similar candidate replaced him.

Because that core scenario never occurred, we cannot definitively say whether the Democratic establishment would have used superdelegates and other primary‑process controls to stop such a candidate. There is suggestive behavior (rule‑rigging accusations, no debates, later use of superdelegates to manage the Harris nomination, aggressive tactics against RFK Jr. as an independent), but no direct, decisive case of an insurgent Democrat being blocked at the convention.

Therefore, the prediction’s truth value is ambiguous: there is circumstantial evidence consistent with Sacks’s expectations about establishment behavior, but the specific “if X, then Y” scenario was never actually tested.