The 1998 Alabama gubernatorial election was the only Republican runoff that — like the race in Mississippi — included an incumbent, Gov. Fob James, and James gained ground between the general election and runoff. James, however, was leading after the first round. The only Senate runoff during this period to feature an incumbent was on the Democratic side, Arkansas’s 2010 election. Blanche Lincoln slightly expanded her lead.
So we can’t confidently say Cochran has an advantage in the runoff because he’s an incumbent, and we can’t confidently say McDaniel has an advantage because he led — barely — the general-election voting. But runoffs also provide an extra campaign time; in Mississippi’s case, the candidates have a bonus of almost three weeks. Does that time benefit lesser-known candidates by giving them more exposure?