Send in the US Army.
Re: How would he do so, legally, with liberal courts? He ordered the national guard to defend, and the governor of California refused.
As President, Trump has significant discretion in how USA immigration laws must be enforced, or not enforced.
Prime Example: Obama’s legal DACA policy
Trump had two weeks notice to write a new refugee policy and to get his legal team in place to block this invasion.
Instead, Trump did nothing.
Which means tens of thousands of new "refugees" will quickly follow.