The president has received a great deal of criticism from Democrats and even from some Republicans for winding down President Obama's 2012 executive order which granted temporary resident status to young immigrants brought illegally into this country. The program was called Deferred Action for Childhood Arrivals (DACA) and affects almost 800,000 people. For an excellent summary of what DACA does and why President Trump has rescinded it see this piece at CNN.
The criticism of President Trump's decision is misplaced as Rich Lowry argues at National Review. It is not the president's prerogative to circumvent Congress in creating immigration law, which is precisely what President Obama did when he made DACA official policy. Indeed, he did it after acknowledging on numerous occasions that he lacked the legal authority to do so, which makes his criticism of President Trump's order to undo DACA awfully hypocritical.
President Obama also stressed that what he was doing in creating DACA was only temporary and that eventually Congress would have to pass legislation to resolve the status of the so-called "Dreamers."
All President Trump has done is to tell Congress that Obama's original order was expiring, and that it's time for them to do their job by passing legislation that addresses the situation that the Dreamers find themselves in. The president, after all, is not a monarch who can create law through arbitrary exercises of executive power. We're a nation of laws, a Republic in which the people decide through their elected representatives what our immigration policy should be.
Trump ended DACA because he promised in the campaign that he would and because a number of states were threatening to sue the federal government over DACA, a suit they would very likely have won because DACA was, according to most analysts, an unconstitutional executive usurpation of Congress' authority by President Obama. That even liberal Democrats recognize this was made clear on a segment of a show on MSNBC, which is probably the most progressive/left of the cable news outlets.
On the show the host repeatedly challenged a Democrat congressman who supports DACA to explain how it meets constitutional muster. The congressman could not, or would not, answer the question:
The DACA young people, some of whom are actually in their thirties, are in a tough spot and Congress should find a compassionate way to resolve their predicament without doing an injustice to all those who seek to come into this country the proper way. Congress would find a lot of support for leniency in this country if they also insured that our immigration laws would henceforth be rigorously enforced.
A good start would be to cut federal funding to any municipal entity or school that prevents immigration authorities from doing their jobs.