4. Institutions themselves fail.
The Constitution’s system of checks and balances sets the various branches against each other for the laudable purpose of constraining tyranny. However, due to partisan polarization, individual corruption, or any number of other reasons, sometimes the political institutions in these arrangements fail, sending the governmental system into a crisis. This was the type of constitutional crisis commentators were seemingly referring to in describing reports that Customs and Border Protection agents (members of the executive branch) weren’t following orders from the judicial branch.
In theory, clashes between different parts of government could regularly produce constitutional crises, but in reality, they often don’t. Had Nixon ignored the Supreme Court ruling ordering him to turn over tapes of conversations he had recorded in the Oval Office, that would have been a huge crisis of this genre. But he didn’t.
Government shutdowns are a milder example. During the brief shutdowns in the Clinton and Barack Obama years, some government functions remained in place, and in both cases, agreements were eventually reached. But these situations illustrate how the Constitution doesn’t always provide safeguards or guidelines for making a decision when governing bodies reach a stalemate. The provisions of the Constitution set up political incentives for elected leaders to ensure that the government runs. When these don’t work, there’s not much recourse.
True constitutional crises are rare.