This is an astute observation, and if I may I’d like to add to it.

When evaluating a news source for whether it’s unbiased, left or right, we necessarily look at the stories it presents and check whether they align with and present in a positive light a particular political option.

We call it „unbiased” if it doesn’t particularly favor any of these.

We’re already in the realm of US electoral politics - for a second we can assume that nothing else exists.

In 2016 the political landscape shifted drammatically and presenting the „right wing” option in a favorable light required certain concessions when it comes to previous journalistic standards.

So, just by sticking to its previous guidelines, the AP would automatically shift to the „left” - because the landscape changes.

It would be more accurate to say that the world shifted underneath AP’s lense and so it immediately started being perceived as left wing.