I trust you have examined all the asylum claims of those at the border to have made your sweeping finding outlined in your last two sentences above. For my part, I worked professionally and opined on these issues, individual claims, detention conditions, and policies for 20 years under Reagan, Bush 1, Clinton, a bit of Bush 2, plus volunteering a bit under Trump. I addressed asylum officers, and submitted testimony to Congress. To roughly quote the Refugee Act, anyone within the United States, or at a land border or port of entry can apply for asylum, irrespective of their immigration status. See section 208 (a) at the link below. Reagan's administration was terribly biased on asylum cases, but not even he proposed what Trump did.
Trump proposed simply sending people back without a process at all, a violation of the law. He proposed returning people who had fled non-government entities connected to the government or which the government could or would not control, like the Mujahedeen in Iran. This would have violated decades of precedent, dating back to the early 1980s, honored under all the president's named above, plus Obama.