Illegal immigration was already way down and continuing to drop. It was a trend in the making before trump took office that has simply continued. Please get out of the fantasy world where trump came along and the previously spiraling out of control illegal immigration problem immediately reversed and dramatically dropped. That simply isn't true.
As for the wall, it would be a gigantic useless waste of money. The wall simply won't do a damn thing. Why? Because not only will those intent on coming across our southern border find a way around, over or under the wall, but they only represent a small portion of the folks in this country illegally. Most of the undocumented come here legally and simply overstay their visas. How's your precious wall gonna stop that? And one more thing... we were promised that Mexico would pay for the wall. PERIOD. He said it time and time again and it was a cornerstone of his campaign. So anything short of Mexico actually paying for the wall is completely unacceptable. Face it, you and all the other Trumpanzees (I know I know... you aren't a trump supporter and didn't vote for trump ) have been conned.
Your first paragraph is inaccurate as I nowhere attributed falling illegal immigration to Trump, although he may have expedited its existing decline. Secondly, it will not be easy to get under, over or through the wall. There is no basis for that claim. Thirdly, if people crossing the border illegally only represent half, or even 40% of illegals, isn't it worth cutting that to a trickle? Fourth, I've said before that we need to be able to track and deport people here overstaying their visas. That's all part of the effort. Lastly, no, Mexico isn't writing us a check for the wall. I've never indicated that and I'm not sure too many people actually believed it. It will be paid for in savings from keeping them out to begin with. Oh, and despite what you think, I didn't vote for Trump in the primary. I didn't vote at all in the general election.