“Picking a side” does not mean you must disagree on everything. However, in today’s political highly-charged political environment, “picking a side” does mean being able to make a decision which of the two major political parties represents your values best, and which one will take the country in the direction you think it needs to go.
While I might some areas of common ground with a Democrat running for office, it’s not nearly enough that I would ever back one of them for any elected office, as all Democrats tend to march pretty much in lock-step with the Democratic Party agenda, and I want to suppress the Democratic Party agenda, as I do not like the direction they want to take our country.
So, “picking a side”, the Democratic Party or the Republican Party, is a very easy choice for me, as I find the Democratic Party agenda to be extremely racist, anti-American, and anti-science.
Therefore, I do not have any trouble whatsoever picking which “side” to back.