Illegal immigrants do not cause exploitative employers to put Americans out of a job. Rather, the toleration of exploitative employers is what creates the demand for illegal immigrants.
To illustrate this, look to Europe. In August, your correspondent was standing on the seafront in Calais, France, asking young penniless Africans why they were so desperate to hitch a ride over the channel, when France is just as wealthy as Britain. The answer is actually simple. In France, finding work without an identity card is extremely difficult. That is why in Paris, unlike in London, tourists often find themselves accosted by African men selling beads or running scams. Africans living in London without paperwork don’t need to sell trinkets to get by: they can find better-paid work cleaning offices.
Eric Posner’s read on the situation:
Republicans are right about one thing. Obama’s action will not fix the problem of illegal immigration; nor would congressional action that created a legal pathway to citizenship. The great irony is that as undocumented aliens gain rights, they will no longer need to, or even be able to, supply menial work at a low wage. Illegal immigration will rise again, just as it did after the last path-to-citizenship-law in 1986. America’s hunger for cheap labor can’t be legislated away.