Market returns after elections

Ken Fisher did a recent video where he explains the "Midterm Miracle": the nine months starting in a midterm year's fourth quarter and running through the next two quarters. Over the last century, this has been the most consistently profitable stretch in stock market history.

YouTube: Ken Fisher’s 2026 Midterm Election Forecast (Fisher Investments)

Seems this is a widespread notion that I somehow have never heard of.
I have the historical S&P 500 data, so it is not difficult to plug it into a spreadsheet and see what comes out.

Elections happen every 2 years, on even numbered years.
Presidential elections are every 4 years.
Midterm elections are every 4 years, 2 years after the presidential election.
The President's party almost always loses Congress in the midterm elections.

The S&P500 returns for all the 3 quarters periods 1985 to 2026, lined up with election years:

        Every 3 qtrs  Elec yrs  non-elec yr  Pres elec  midterm elec
Avg:      7.7%        13.3%     7.2%         8.3%       18.3%
Min      -47.5%       21.2%    -16.2%       -21.2%       1.0%
Max       49.0%       35.0%     37.8%        28.8%      35.0%
Median    8.5%        14.1%     6.6%         9.7%       18.6%
count                 20        20           10         10

Election years show larger than average returns and midterm years show much larger returns.

For & the entire modern period beginning after WW2.
The returns for all the 3 quarters periods 1950 to 2026, lined up with election years:

        Every 3 qtrs   Elec yrs  non-elec yr  Pres elec  midterm elec
Avg:      7.0%        13.2%     4.4%         5.8%       20.1%
Min      -47.5%      -21.2%    -21.9%       -21.2%       0.4%
Max       53.5%       49.8%     37.8%        28.8%      49.8%
Median    7.7%        15.5%     4.5%         5.7%       18.4%
count                 37        37           18         19

The relative performances are consistent.

It is hypothesized that when Congess and the President are held by different parties, that this causes political deadlock. And the market loves deadlock because no major economic law changes can happen.
That's the theory of why the 3 quarters beginning with Q4 of midterm election years have high returns.