Border Patrol agents nabbed about 168,000 people crossing at the southern border in March, a 20-year high. Yet neither President Joe Biden nor Vice President Kamala Harris, who he’s put in charge of dealing with the “root causes” of the migrant surge, has deigned to visit the border — or, indeed, done anything to address the crisis, including its “root causes.” It’s clear they simply don’t care. Biden’s “border czar” last month admitted the administration has been sending “mixed messages” to migrants. Was that honest frustration part of why she announced her resignation Friday, not even three months into her tenure? Central Americans don’t seem to think the messages are mixed at all: The number of illegal-migrant encounters at the border rose more than 71 percent from February to March because Biden’s policies say “Come on in!” His first day in office, the prez ordered the end of all wall-building at the border and a 100-day pause on deportations. And he hasn’t looked back, despite the record-high numbers of migrants and, worse, unaccompanied minors in federal custody. His 2022 budget plan calls for a 16 percent hike in domestic spending — but not a cent for border security.