Not that the Union-Trib would tell their readers, but Roberts is a (shhhh!) democrat. If this had been a Republican, the R word would have appeared in every paragraph.
No, he was a Republican. The runoff for SD mayor in 2004 was between two Republicans (Dick Murphy and Ron Roberts), which is why Democrat Donna Frye, running as an unallowed write-in candidate in the runoff election, got around 30% of the vote.