What historical Senate impeachment trials explain the two‑thirds convicting threshold and its political dynamics?
Executive summary
The Constitution’s two‑thirds convicting threshold for Senate impeachment trials was designed as a high political bar to ensure removal from office only with broad consensus, a principle the Framers and early commentators articulated and the Senate has repeatedly enforced in practice [1] [2]. Key historical trials—Samuel Chase (early Republic), Andrew Johnson , William Belknap , Bill Clinton , and Donald Trump’s second trial —illustrate both the Framers’ theory and the messy political realities that make two‑thirds a decisively political rather than purely legal hurdle [3] [4] [5] [6].
1. The Framers’ safety valve: why two‑thirds was written into the Constitution
The two‑thirds requirement emerged from a deliberate decision to separate the accusatory power of the House from the convicting power of the Senate, a structural check meant to protect officials from partisan persecution and to demand cross‑factional agreement before removal (Federalist No. 66 summarized in the Constitution Annotated) [1] [2].
2. Early practice — the Chase impeachment and the principle tested
The impeachment of Supreme Court Justice Samuel Chase turned the abstract constitutional design into practice by foregrounding whether political disagreement should translate into removal, a contest that helped crystallize the view that impeachment is political and that the Senate’s high threshold guards judicial independence by making conviction difficult without broad Senate consensus [3].
3. Andrew Johnson: the archetype of narrow, partisan failure
Andrew Johnson’s 1868 trial remains the classic example of the two‑thirds rule’s political consequences: the Senate needed 36 guilty votes to reach a two‑thirds majority but fell short by one, with 35 guilty and 19 not guilty—an outcome produced by intra‑party defections and intense factional maneuvering that left the president politically neutered but legally in office [4] [5].
4. Belknap and the jurisdictional wrinkle of resignation
The Belknap case of 1876 showed that the Senate’s political choices about jurisdiction and post‑resignation trials matter: although Belknap resigned before the House impeached him and a majority favored conviction in the Senate, no article achieved the two‑thirds threshold, producing acquittal and underscoring how the numeric supermajority, not just a majority sentiment, controls outcomes [3].
5. Clinton and Trump: modern partisan polarization meets the two‑thirds wall
In the late 20th and early 21st centuries, Bill Clinton’s 1999 acquittal and Donald Trump’s second impeachment trial in 2021 both demonstrated that even when majorities in the House and significant Senate blocs favor removal, the two‑thirds requirement often prevents conviction; Clinton survived without reaching the 67 votes needed, and Trump’s second trial saw 57 guilty votes—short of the 67 required—despite bipartisan defections [5] [6] [7].
6. The two‑thirds rule as politics masquerading as constitutional law
Across these episodes the practical dynamics are consistent: the Senate sets its own trial procedures, rules, and evidentiary posture, and because conviction is a supermajoritarian political act rather than a standard criminal verdict, outcomes turn on partisan math, cross‑party defections, and strategic procedural choices—the Framers’ safeguard operates as both a check on factionalism and a brake on accountability, depending on one’s perspective [8] [9] [1].
7. What conviction does — removal and optional disqualification
The constitutional effect of a Senate conviction is immediate removal from office and, optionally in a separate vote that requires only a simple majority, disqualification from holding future federal office; that procedural separation has shaped strategic behavior by senators and House managers in multiple trials [10] [11].
8. Takeaway: a constitutional design that makes politics decisive
The history of Senate impeachment trials shows that the two‑thirds threshold was intended as a stabilizing supermajority to avoid partisan removals, but in practice it transforms impeachment into a political crucible where alliances, defections, and rules control the result—illustrated repeatedly from Chase and Johnson through Belknap, Clinton, and Trump [3] [4] [5] [6] [2].