In "Three Anti-Partisan Constitutional Conventions for Congress" on Concurring Opinions, Prof. Gerard Magliocca discerns three constitutional conventions from the partisan precedents that relate to Congress. He says that at this point in our political development one political party may not:
(1) alter the structure of the judiciary in its favor; (2) use its supermajority to purge judges or expel members of Congress who belong to the other party; or (3) seize control of the presidency or the vice-presidency from the other party without winning a presidential election.
Magliocca acknowledges that these things have happened and are still legal but he says that we now think that they are beyond the pale. Here's hoping.