All three branches operated with minimal institutional infrastructure. Presidents issued a handful of executive orders (Washington averaged 1 per year), Congress passed modest bodies of law with no committee oversight apparatus, and the Supreme Court — deciding under 50 cases annually — was still establishing its basic authority. The JPI for this era is driven almost entirely by caseload, with judicial review appearing only sporadically (Marbury v. Madison in 1803 marks the first law struck down). The EPI and LPI are both near historical lows, and the "balance" is less a tension between strong forces than a shared condition of institutional modesty.

Lincoln's presidency marks the first sustained spike in executive unilateralism — his EO rate was the highest of any president to that point, and the Civil War validated broad claims of emergency authority. Congress responded with aggressive Reconstruction legislation, veto overrides of Andrew Johnson (who issued 29 vetoes, most famously on civil rights), and the first serious use of impeachment. The judiciary scaled up rapidly: the Supreme Court decided over 240 cases in some terms, and began striking down laws at a pace it would not match again until the 20th century. This is the first era where all three indices rise simultaneously — a signal of institutional expansion across the board, driven by national crisis.

This period sees the sharpest divergence between branches. The JPI peaks in the late 19th century when the Court routinely decided 250–300+ cases per term and struck down laws at unprecedented rates (the Lochner era). The EPI spikes dramatically with the Progressive presidents — Theodore Roosevelt, Wilson, and above all FDR, who issued executive orders at a rate of 307 per year and used vetoes at an historic pace. Legislative output swelled too: Congresses in this period regularly enacted 500–700 laws per session, reaching a sustained plateau. The New Deal era represents the most significant power shift in the dataset: executive authority expanded into economic regulation, emergency powers, and agency creation, while the Court initially resisted (striking 8 laws in OT 1935 alone) before capitulating after the "switch in time" of 1937.

The Cold War locked in elevated executive power (EOs, emergencies, recess appointments) while Congress built out its modern institutional machinery. The LPI peaks in the mid-1970s: the 94th Congress (1975–77) scored the highest LPI of any Congress in history, driven by the post-Watergate expansion of oversight, the creation of the budget resolution process (1974 Budget Act), and a record 8 veto overrides of Gerald Ford. Meanwhile, the Warren and Burger Courts sustained historically high caseloads (200–370 cases per term) with aggressive constitutional activism, creating the highest sustained JPI readings of the modern era. This is the only period where all three branches simultaneously register high composite scores — genuine tripartite engagement.

The modern era is defined by divergence. Executive power has intensified through presidential memoranda, emergency declarations, and regulation — the EPI for the last four administrations (Obama, Trump I, Biden, Trump II) averages well above the historical mean. Legislative output has contracted: modern Congresses enact fewer than 400 laws per session (down from 800+ during the Cold War), though new tools like the Congressional Review Act have opened novel channels of influence — the 119th Congress has already enacted a record 22 CRA resolutions. Judicial throughput has collapsed: the Roberts Court decides 60–80 cases per term (vs. 250+ a century ago), but strikes laws and overrules precedent at higher per-case rates than any prior era, producing outsized constitutional impact from a shrinking docket.