Leaving Harry on the Doorstep

[pippin_999]

No: HPFGUIDX 158637

Dumbledore mentions in HBP that it is unwise to linger on the
doorstep. That being the case, I don't think he really left the
area when he vanished after re-lighting the lamps in PS/SS.

Canon  states that with a swish of his cloak he was gone,
but since he was standing at the corner, not the doorstep, he
could well have apparated back to the house and remained 
there, invisible,  until Harry was discovered.

I suspect that Petunia had refused or ignored Dumbledore's
owls, including perhaps the tawny one that fluttered past the
window during breakfast, and leaving the baby at the door
was a last ditch effort to persuade her to take him. I doubt
Petunia could stand the thought of the scandal that would 
ensue if anyone else discovered a baby had been left in
such a fashion. No one would believe it was her sister's
child, particularly as she was pretending she didn't have
a sister. 

So, for the sake of Vernon's reputation, she had to get 
Harry off the steps. But that sealed the charm, and from 
then on she was riding the tiger. Whatever happened, the
people who killed her sister and had tried to kill Harry
would know that she had given him protection, and
they would seek revenge. As long as she was protecting
Harry, the WW had a reason to defend her. But if she
stopped, there would be other priorities...

Pippin