And the 20th amendment gave Congress the process to deal with the "failure to qualify" of either or both of the President and Vice President within that same timeframe.
Why does nobody want to include the 20th amendment's election process when discussing Article II and the 12th amendment? It's just as relevant as the others, but it seems to be kryptonite.
At the time of the joint session of Congress to open the Electoral College votes, the 20th amendment could have been invoked, declaring that Biden and Harris "failed to qualify," and that the Congress would either appoint someone to act as President in the interim, or just keep the current President in office until the qualifications are resolved. That would have been an entirely constitutional thing to do via the 20th.
We're past that now, but it would have been the thing to do at the time.
-PJ
As I see it, the "failure to qualify" provision of the 20th Amendment can't be based on some arbitrary decision in a political or legal process that isn't already in place under the Constitution and/or Federal law. In other words, Congress doesn't have the authority to simply decide on January 6th (for example) that Joe Biden doesn't qualify to be the President because someone in Congress (or the Vice President, acting as presiding officer over the joint session) says so. Rather, the "failure to qualify" can only be established AFTER the Article II and 12th Amendment process has played out. One scenario that might apply here would be where the electoral vote in December produced no majority for any presidential candidate (suppose the Libertarian or Green candidate won a handful of swing states, for example), the presidential election was passed to the House under the 12th Amendment, and at the January 6th session of Congress the House vote for President ended in a tie. That is certainly not outside the realm of possibility when you have an even number of states, and/or you have state House delegations that are split evenly between Democrat and Republican representatives.
As it relates to what I just posted, I don't dispute this except insofar as what exactly it means for Congress to "invoke" the 20th Amendment. I don't see the 20th Amendment as a mechanism for Congress to simply decide arbitrarily that a candidate "fails to qualify" for President.