I think this is what you're looking for.
The Constitution lays this out in two parts.
Article II Section 1 says "Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector."
The 12th amendment says "The person having the greatest Number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed..."
If a state fails to appoint electors, then the majority of appointed electors goes down. If Pennsylvania (20 EV) fails to appoint its electors, then the number of appointed electors drops to 518, and the majority becomes 260 EV to win.
People are stuck on the number 270, but that assumes a FULL Electoral College. If a state fails to certify, and fails to APPOINT its electors, then they simply don't participate in the Electoral College. In that case, the Electoral College is not bound by a 270 threshold. That threshold is reduced to a majority of the APPOINTED Electors who do participate.
This is where Article II offers the remedy:
If a state thinks it's in risk of defaulting on its Electoral College participation, then the legislature can exercise its plenary power to call a special session and choose to directly appoint their Electors, regardless of how the state's citizens voted.
-PJ
In the Senate, only one-third of the seats are up for election. If those same states can't certify a Senator (apparently for the same reason they couldn't appoint Electors), the governor MUST appoint a replacement to fill the vacancy because Article V says "no State, without its Consent, shall be deprived of its equal Suffrage in the Senate." The Governor can choose to not appoint a Senator, leaving the state with reduced Senate representation.
And, since the entire House is up for reelection, there will be no House on January 3 to select a Speaker. More likely, the Republican states that do not use mail-in ballots will have ordinary elections and send their Representative to the House; they will not be affected by counting delays. It will be the Democrat states that can't count and certify their elections that will leave vacancies in the House. The Republican majority of those present will choose their Speaker.
-PJ
One thing to keep in mind: While the Constitution says electors are appointed in the manner the Legislature chooses, the courts have also held that the method for choosing the electors has to be selected prior to the votes being cast. So you couldn’t have a case where the method of selecting electors was by popular vote (which is true of all states right now), and then have the legislature deciding to have the governor or legislature appoint the electors directly after the vote has been held. Any such changes would only apply to subsequent elections. You can’t change the rules after the game has started.
Nice summary, thank you!
Good food for thought.
You need to read 106 as well.
Seeing more of the pattern.