On textbook-writing: I do not have intimate knowledge of how history textbooks are written, approved, and adopted. However, I will say that most historians, especially when it comes to the classroom, are looking for causality. The events that are prioritized are the ones that can be tied most closely to causing-- directly or indirectly-- other events. A good history textbook is scaffolded around causality, helping students understand how each "era" (or whatever unit of time is being used) evolved into the next. So if I had to predict what gets written down from the Trump presidency, it would be those events which historians can tie into, well, later events that have not yet happened.

For that reason, it's hard to say how these years will be presented. Will "Russiagate" feature heavily? Maybe, if U.S.-Russia relations change dramatically over the next decade. So it's tough to definitively say. COVID will certainly be in there, but its effects on the development of the world have not yet been established. So basically, we won't know until we know.

On objective history: in your question you discuss the intense polarization of society. Right now, it can be difficult to even see Democrats and Republicans sharing an understanding of reality itself. But it is the work of future historians to assemble the evidence after an event and draw out the truth, as well as make the causal connections that I mentioned. Previous eras of extreme polarization-- for example, at the turn of the 18th century-- probably felt, to the people living in them, similarly unhinged from shared reality, but historians have parsed the evidence and found factual details. Today, textbooks can recount that era without partisan shading.

Now, you may be wondering, how can we trust those future historians to be objective? How can we trust their causal stories? And the answer is, we can't, really. A lot of history is about making arguments about how something is best understood. There's room at the primary research phase for subjectivity and bias-- what details are you prioritizing? How is the causal explanation you are arriving at informed by your personal biases and motivations? Add to this that textbook writers usually have to choose one causal story and run with it, and you realize that objective history is... kind of impossible. Life is really, really complicated. And good history tries to make sense of what the hell happened in the past with causal stories and adherence to as much detail as possible. But ultimately, I'd argue history can never be fully objective. That's part of why history is always being written: if we actually could write exactly what happened and why, we wouldn't need to. But history as a discipline is a constant searching and searching for deeper and fuller understandings of the past.