I think the polls undercount his support by roughly 2 to 2.5%. And of course, his support is weaker on the edges and stronger in the centre of the US, exacerbating the discrepancy regionally, which is important in adding up the electoral college.
This bulge is not enough to defeat a popular candidate like Biden. But it was enough to defeat HRC with Comey's disastrous intervention last time.
I suspect the folks in the middle collectively have a major inferiority complex, which Trump claims to cure for them. But actually, it just makes them the victim of his con.