in the saddle
US /ɪn ðə ˈsæd.əl/
UK /ɪn ðə ˈsæd.əl/

1.
掌權, 負責
in a position of control or responsibility
:
•
After the CEO retired, his successor was quickly in the saddle.
首席執行官退休後,他的繼任者很快就掌權了。
•
With the new manager in the saddle, we expect significant changes.
新經理掌權後,我們預計會有重大變化。