"The ace in his vest"

In her Letter from an American for 29 July, Heather Cox Richardson accurately refers to voter suppression laws as "the ace in his vest" for House Minority Leader Kevin McCarthy's goal of becoming Majority Leader after the midterm elections in 2022. I was surprised by this construction, as I have always seen the idiom as "an ace up one's sleeve". The OED dates the "sleeve" form to the mid-nineteenth century and doesn't refer to the "vest" form, but some further internet searching turned up a few other examples with "vest", especially as "an ace in his vest pocket". Indeed, the pocket would perhaps be the best place to conceal a card. (Andrew Shields, #111words, 30 July 2021)

 

One of many stock photos of "an ace up his sleeve".