I've found out that it was first published in 1903 as part of Shapes of Clay, but Bierce writes in the preface that "Many of the verses in this book are republished, with considerable alterations, from various newspapers".
For that reason, I'm tempted to choose 1900 as the first appearance of the poem, based on the lines 13-14:
"For to-morrow will by Monday and the fifth day of November--
Only day of opportunity before the final rush.
which seem to suggest 6 November 1900 presidential election, although 1888 also seems possible.
Can anyone provide concrete information to earliest date of poem's first appearance/incarnation?