to get sth open by tapping or striking it · (figuratively, when followed by sth like ∼的大門|∼的大门 xx de dà mén) to open the door to ~ · to gain access to ~

It drew strength from the not-so-young people who braved the bitter cold and scorching heat to knock on doors of perfect strangers, and from the millions of Americans who volunteered and organized and proved that more than two centuries later a government of the people, by the people, and for the people has not perished from the Earth.