MD has a closed primary in which unaffiliated/independent voters cannot vote. Yet Nikki Haley managed to get 20% of the R-primary vote.
Haley got 33% in Howard county, 31% in Montgomery County, 26% in Prince George’s county and about 25% in Anne Arundel county. All DC - Baltimore suburban counties.
Yet another example of Trump’s weakness in in the suburbs, which have a higher share of college-educated voters.
Or, these are protest votes and they'll come home in the general.
I've heard analysis to the effect that people who are motivated to come out and vote against Trump after the outcome has already been decided can be counted on not to vote for him in the general. If they don't vote for Biden they'll probably either make a protest vote or stay home.