Two things you need to know about trends in US party affiliation

A new Gallup poll raises some old questions about sampling error and non-response

Here are a few paragraphs from a recent CNN article covering a new Gallup poll that shows the Democratic advantage in party affiliation is the largest since the party’s 2012 lead:

This is a *major* warning sign for Republicans….

Gallup polling for the first three months of 2021 shows that 49% of the public identify as Democrats or Democratic-leaners, while just 40% call themselves Republicans or say they lean toward the GOP.

That's the largest gap between Democrats and Republicans in Gallup's quarterly study of party identification in nearly a decade. The last time Democrats had a larger lead on party ID was early 2009…

But it's not just the party ID gap that stands out in Gallup's first-quarter polling. It's this: Just 25% of the public calls themselves Republicans -- close to the lowest (22%) that Gallup has ever measured since it started doing telephone-based polling. (Another 15% say they lean to Republicans.)

When you combine those two data points, you get this: Not many people want…