The article includes a description of Palmer's background:
Given Palmer's background, I am certain he is well aware of the absurdity of his political analysis. No
doubt he is simply doing what so many conservative commentators are doing these days, telling their audience what they want to hear rather than the far more painful truth. (For another recent example, take Newt Gingrich's piece "The Red Wave is Growing.")
In analyzing election results, you compare apples to apples, oranges to oranges. Mid-term elections get compared to mid-term elections. Presidential election years get compared to other presidential election years. Why? Those elections feature starkly different electorates. Likewise, those who turn out for a general election are far different than those who turn out in the primary which proceeded it.
That is a phenomenon I personally experienced while running for the House in 2000. I won the primary for the northwest Indianapolis district. My Republican opponent and I combined had the primary vote than did the Democrat. But on the day of the general election, I did not beat my opponent 2-1, but rather only received, rounded off, 40% of the vote. What happened? Different electorate. Voters did not like George W. Bush in that district, and they turned out in droves to vote against him. My candidacy experienced the collateral damage of increased Democratic-leaning turnout spurred by a race at the top of the ticket.
Again, no doubt Palmer is well aware of the silliness of extrapolating primary vote to predict general election results. But the primary election results can be used to measure partisan trends in those California Congressional districts. In employing the apples to apples, oranges to oranges principle of political analysis, I have compared the aggregate partisan primary turnout in 2014 compared to 2018 in the key California districts at play this fall. Below is what I found.
These tables show that while both parties experienced much higher primary vote in 2018 than 2014, the Democrat primary vote share increased in every district, some districts significantly. That is consistent with the markedly increased Democratic turnout that has has been seen in virtually every special election race since the 2016 presidential election. Primary results do not mean the Republicans will lose those districts, however. Again, the general election electorate is much different than the much smaller turnout that happens in a primary.