It appears to be one of the "patriotic" versions of Jacksonian buttons. You'll see a very similar "patriotic" one (American eagle with shield) at upper right in the group-photo below. I'll include another photo, showing one whose emblem is an even closer match to yours.
Jacksonian buttons are an early form of 2-piece button, consisting of an applied brass rim around a brass 1-piece flatbutton. They get their name from becoming widely popular during the first term of US President Andrew Jackson (1829-37). All Jacksonian buttons are civilian-usage, not military, although a few have a "patriotic" emblem, like yours. As you'll see at the Jacksonian buttons webpage, most have a civilian emblem, such as a plant or animal.
All of the Jacksonian buttons are either vest-size or cuff-size... there are no coat-size ones (20mm or bigger). Yours being a cuff-size adds weight to the likelihood of it being a Jacksonian button.