1
general::
Also, hold all the trumps. Be in a winning position, as in We can't argue with Jeff; he holds all the aces, or If Jean refuses, he'll reveal that he holds all the trumps and force her to give in. These expressions allude to card games in which the ace or a trump card outranks all the others. Also see PLAY ONE'S CARDS RIGHT; TRUMP CARD.
American Heritage Idioms
2
general::
Phrase(s): hold all the aces [and] hold all the cards
to be in a favorable position; to be in a controlling position. (Alludes to having possession of all four aces or all the high cards in a card game.) • How can I advance in my career when my competitor holds all the aces? • If I held all the aces, I’d be able to do great things. • I tried to get my points across, but Joan held all the cards and the board voted for her plan.
McGrawhill's American Idioms And Phrasal Verbs