The argument in one screen
Partial intermixture can be proper
Hamilton rejects the idea that separation of powers forbids every special overlap. Some overlaps are necessary for checks and mutual defense.
The House accuses, the Senate judges
Impeachment power is divided, not concentrated. Hamilton treats that division as a core protection against persecution and confusion.
Two-thirds for conviction protects innocence
The supermajority requirement is presented as an added security against factional condemnation.
The Senate is not the whole government
Hamilton answers the fear of senatorial predominance by pointing to the House's role, other counterweights, and the need to examine each power in context.
Why Hamilton thinks the separation-of-powers objection overstates the problem
Critics say the Senate as impeachment court mixes legislative and judicial authority in one body. Hamilton replies that this objection depends on an overly rigid reading of separation of powers.
That is why Federalist 66 matters. It turns the argument away from slogans and toward constitutional function. The question is not whether any overlap exists. The question is whether a partial overlap serves a defensible check without collapsing the larger distinction between departments.
Not a denial that mixed powers can be dangerous. A claim that some carefully structured mixtures are part of how constitutional self-defense works.
“The true meaning of this maxim has been discussed and ascertained in another place, and has been shewn to be entirely compatible with a partial intermixture of those departments for special purposes, preserving them in the main distinct and unconnected.”
Hamilton says separation of powers does not forbid every carefully bounded overlap. The real question is whether the overlap serves a specific constitutional function without dissolving the larger distinction.
“This partial intermixture is even in some cases not only proper, but necessary to the mutual defence of the several members of the government, against each other.”
That is Hamilton's core structural answer. Some overlaps exist not to erase boundaries, but to help each part of government defend itself against encroachment by the others.
“To an objection so little precise in itself, it is not easy to find a very precise answer.”
Hamilton says vague fears of senatorial predominance should be replaced with a more disciplined method: examine each power on its own merits and ask where it can be lodged with the least inconvenience.
How Hamilton builds the case
He first answers the maxim itself. Separation of powers does not mean every department must be sealed off from all others in every respect. Hamilton says some partial intermixture is proper or even necessary when it gives branches a constitutional means of defense against encroachment.
He then points to the structure of impeachment. The House alone impeaches, the Senate alone tries, and conviction requires a two-thirds vote. That arrangement, he says, avoids making the same body both accuser and judge while also protecting innocence against factional excess.
Finally, he answers the aristocracy objection by refusing vague arithmetic of influence. The better method, Hamilton says, is to ask where each specific power belongs with the most advantage and least inconvenience. On that practical comparison, the Senate remains the most fit place for impeachment trials.
He defends overlap as constitutional function
Hamilton does not celebrate institutional blur for its own sake. He defends it where it creates a needed check and preserves the larger separation in the main.
He relies on division plus supermajority
The House-Senate split and two-thirds conviction rule are the main structural devices that answer the persecution objection.
He rejects vague influence arithmetic
Instead of asking whether the Senate gets “too much” in the abstract, Hamilton wants readers to examine each power concretely and comparatively.
Federalist 66 matters because it explains why constitutional checks sometimes require limited overlaps of function. Hamilton says the Constitution can remain a separated system in the main while still mixing powers in carefully chosen ways for special ends.
The essay also matters because it shows how Publius often answers criticism: by dissolving broad alarm into a more specific institutional comparison and then asking what realistic alternative would work better.
Why Federalist 66 matters in the larger Senate sequence
Federalist 65 argued that impeachments are political offenses and that the Senate is the most fit tribunal available. Federalist 66 answers the next wave of objections by explaining why that arrangement does not fatally confuse powers or create a senatorial monster.
The sequence is now moving from the Senate's general character to Hamilton's executive turn. Federalist 67 starts that transition by rejecting the claim that the President is a disguised monarch, and Federalist 68 explains the constitutional design of presidential selection. For the wider Publius frame, return to Who wrote the Federalist Papers?.
What to read next
Primary sources and further reading
- The Federalist No. 66 | Founders Online — Hamilton's answer to objections that the Senate trying impeachments improperly mixes powers or accumulates too much influence.
Related essays by theme
Use Federalist 66 to understand why constitutional checks sometimes require limited overlap
This is the essay to read when you want Hamilton's cleanest answer to the claim that the Senate trying impeachments breaks separation of powers. His response is that the arrangement is divided, guarded, and functionally justified.
Not a legislative trial court. A narrow constitutional check. Hamilton's defense of Senate impeachment still frames the institutional design.