If the president can choose to enforce some provisions of new laws, while not enforcing others – as he has done with the Obamacare bill – why should we believe that he will enforce the border control provisions of the immigration bill?
Wouldn’t it be much more likely that he will enforce the ‘path to citizenship’ portion vigorously, while totally ignoring anything resembling border control?
After all, the point of granting citizenship (sorry for being so cynical) is that Hispanics mostly vote for Democrats.* Having achieved the goal of adding ten million or so new Democrats to the voter rolls, why then would he wish to do anything that keeps out future Democrats?
Regarding the first paragraph, here's a law professor arguing that the president can't, in fact, refuse to enforce laws when it's inconvenient to do so. I would think that was self-evident, but he's getting away with it, isn't he?
The core of the argument is that the Constitution (Article II, Section 3) says that the president "shall take Care that the Laws be faithfully executed." Note that it says 'shall' not 'may'.
*The Republicans who support the bill have been quite open that the reason they do so is because they hope Hispanics will then start voting Republican more often. Neither party cares much about the right/wrong or good/bad of the proposal.