push against an open door

bang down the door

To present oneself as a strong candidate for a role or achievement, explicitly or implicitly.

close the stable door after the horse has bolted

To attempt to prevent a problem that has already occurred; to design and implement a preventive mechanism that is too late (after the first failure instead of before).

darken a church door

To go to church to attend a service.

darken someone's door

To arrive at someone's residence or location, especially as an unexpected visitor.

don't let the door hit you on the way out

Used as a command to leave in haste, or to indicate that one is glad, or at least unmoved, to see the addressed person leaving.

get one's foot in the door

To initiate contact or a relationship; to gain access, especially to an entry-level job.

get the door

To open a door to help another person to pass through.

go in the out door

To engage in anal sex.