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The graph represents legal entries, which you said were prevented when Biden "inherited" Trump's 42.
I am pretty sure I mentioned some exceptions to immediate expulsion were made. Do you want me to look up the details for you? One example was unaccompanied children. In addition, iirc, limited numbers of Haitians and Cubans were allowed to apply for some sort of protected status.
The majority were sought entry through official ports of entry were immediately sent back. This encouraged them to enter illegally between the borders.. if they got caught, they were immediately sent back, so they would just try again. I am thinking most were single adults.
Hope that helps..