He still is polling up in many polls because unchecked immigration is a bigger issue than we are lead to believe. People see it. To get the poll numbers and reaction the issue of illegal immigration hit a nerve on both sides. Just bringing up the issue instantaneously puts many into a defensive posture because they know what's been going on but can't believe anyone has the audacity to talk about it, they thought illegal immigration was like fight club-never talk about it. Then you have those that have been paying attention to the issue going 'finally, someone willing to talk about it, deal with it'
Like it or not Trump has the best solution to stall and reduce illegal immigration. Secure the border 100% or as close as possible. Without a defined and secure borders any country is that much less of a nation. Amnesty, penalties and deportations are associated issues that need dealing with but securing the borders is half the battle. To me the second half is follow through on enforcement of existing laws and procedures to deal with illegal aliens. That doesn't mean they can't speed up or enhance the legal immigration process.
The RNC just wants to appease their desired voter which makes them wishy washy and quite frankly ineffective. The DNC is doing the same with corporate America which is why Bernie Sanders is showing strong support now. In the end the establishment leadership in both parties will put us in a time machine to the 1990s.