To his base, Trump represents a way of life which they see as being threatened by the changing demographics and attitude of the country — as well as by immigration. There are echoes of the Confederate “lost cause” syndrome in their attempt to maintain a culture characterized by white predominance.
Trump is viewed as the final bulwark preventing a demographic and cultural wave from sweeping the country. As such, it makes no difference what kind of man he is, or the specific policies he enacts, or the level of incompetence he displays, as long as he provides the best chance of holding back the wave.