Not necessary, if you pay attention to the panic in the illegal community when there are even rumors of raids.
Combine that with document checking cooperation with the IRS and SSA, and employer fines/jail-they will leave.
But of course, people who say it's impossible really don't want to try.
I say that if we can't deport illegals (by attrition or otherwise) and protect the our own borders, then we certainly don't have the ability to nation build in Iraq or Afghanistan, and should get the heck out.
There has been no will to enforce the law and there are several reasons for it which have been discussed ad nauseum here. Getting serious about it will change matters but in the end, deporting that many people is not possible. Doesn't mean we shouldn't try when and where possible to get rid of them though.
And, tying the failure to enforce the borders with justifying running away from the WOT doesn't cut it me.