Neither are steadfast. If we relied on either the Legislative or Judicial branch to take action granting cohesive resolve for Confederates post-Civil War - in lieu of Lincoln's 12/8/63 amnesties as a power vested to him through executive pardons, the Union would have collapsed. Outside of amnesty from Lincoln, it took the next acting branch - the Legislative - 7 years after Robert E. Lee's 1865 surrender for their actions regarding the Civil War to be seen (1872 Amnesty Act).

And, in the systematic event that a law is passed that is grotesque - from the legislative, or in the individual event that a miscarriage of law is applied to an individual case - from the judicial; we need a quick check and balance for either scenario - and the Executive branch is (typically, and on average) the fastest-acting branch of the 3. Lest, one bad-faith branch can reliably depend on its complementary power to be too slow to act (which is happening now, in many ways).

As a result, the executive needs to add tension for either event, and just "Legislative <-> Judicial" having checks against one another in relation to laws, and the judicial proceedings concerning the laws, is not enough.

It’s easy to focus on the exceptional cases and say we need “one more level” to be able to override all the other levels. But it’s not clear to me that this is a useful way to frame things. After all, what do you do if you’re “one more level” is the one that commits a miscarriage of justice? What if an executive pardons political or business friends simply for being friends?

Fair point. I am not asking for "one more level". The design already assumes parity. Each branch has a lever to counter the others - some faster than others, and none sits above the rest. Congress has laws, the purse (TBD), oversight, and impeachment. Courts can halt and review. The executive has veto, charging choices, and pardons that reach only federal crimes and never impeachment or civil liability. The whole point of this is when one of three branches misfire, the others answer through state cases, impeachment, elections, or new statutes.

The threat is lateral, not vertical. The system works by equal tension, not hierarchy.

Can impeachment be used to invalidate a federal pardon? My understanding is the President could certainly commit a crime by granting certain pardons, and could be removed by impeachment for that, but the pardon would still take effect over any actions of any branch of government and (arguably more importantly) a jury (which is one of few genuinely democratic institutions).

Short answer is no. Impeachment can remove a president for abusing the pardon power and deter future use, but it does not undo what would otherwise be a valid federal pardon. Once issued and accepted, a pardon binds federal courts and prosecutors. A jury cannot convict on a pardoned federal charge because the case is dismissed or the conviction is vacated.

The "check" to this power itself is also the reach: A pardon does not reach state crimes or civil liability. And the "check" to the person with the power of a federal pardon (the President) is political removal and later criminal charges like bribery - subject to Article 1, Section 3, Clause 7 of the Constitution [1]:

"Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law."

1 - https://constitution.congress.gov/browse/article-1/section-3...