Considering that the Emancipation Proclamation wasn't issued until September 22nd, 1962, that couldn't have been a factor in his nomination. Maybe the use of the word 'later' before 'denounced' might help here...
Yes, that’s a good point. Will fix it.
Anyway, the Democratic Party proudly nominated a man who opposed freeing the slaves.
To be clear, Seymour, before his nomination, was very clear in his opposition to an emanciation proclamation, which had been publicly debated and anticipated before it was actually issued in September 1862.
I clarified the article to say “Seymour would later denounce the Emancipation Proclamation...”
Thanks,