Border security had not become lax prior to Trump. Obama was criticized as the "deporter in chief" by some advocates due to his harsh line on immigrants who had committed crimes. But Obama also benefitted from (and Trump inherited) a reverse migration phenomenon while in office, as more people returned to Mexico than came, due to its improving economy. Trump brilliantly seized on and demagogued an issue with openly bigoted comments ignoring improving facts on the ground. He created chaos at airports within a few weeks of coming to office in one immigration context (his bigotry against Muslims), moved on to lie about overseas refugee processing, and continued that pattern throughout his term in just about every other immigration context What changed during Trump's years was the worsening situation involving drug gangs in Central America, which produced increased migration 3-4 years ago, then the caravan, then the more recent rush to the border. Immigration for Trump did not present problems to be solved or lessened, but opportunities to revive the xenophobia that affects us from time to time. Example: while Trump was railing about us being infested, about Muslims among the migrants, his border personnel were doing their jobs on the border screening in those people with a decent chance at asylum. I volunteered in El Paso last fall and saw its community, ICE, and volunteer visitors calmly doing their best in spite of Trump's rants.
Political genius by Trump and moral bankruptcy go hand in hand. Witness his recent fiund raising scam. Gotta perversely admire his brass balls.e