push at an open door

push at an open door

To easily achieve victory or a desired outcome because it is supported by a majority of people. The area was so entrenched by separatists that the incoming soldiers ended up pushing at an open door. Many assumed that the candidate's seemingly outlandish views would be quickly and decisively dismissed by the population, but it turns out that, in many parts of the country, he was pushing at an open door.
See also: door, open, push
Farlex Dictionary of Idioms.

push at (or against) an open door

have no difficulty in accomplishing a task; fail to realize how easy something is.
See also: door, open, push
Farlex Partner Idioms Dictionary
See also:
  • be pushing at an open door
  • box clever
  • battle out
  • be boxing clever
  • boxing
  • along the right lines
  • under control
  • You can’t win ’em all
  • you can't win them all
  • (you) can't win them all