Fear-mongering is at it's highest right now, but Trump pulls out of Syria while also saying that terrorist are coming in through the borders of Mexico.

I don't have the impression there was EVER fear mongering to get support for the wall.
"No wall" is a position of laziness and apathy, and a "don't care, whatever will happen will happen." attitude.
"Build the wall" is a pragmatic and practical "can do" solutions oriented approach. Frankly it's ridiculously overdue.