And while the district voted for GOP presidential nominee Mitt Romney with 61 percent in 2012, there remains a third possibility that a Democrat can eke into a runoff if the second-tier Republicans carve up the conservative vote.
Operatives say Mayo, an African-American mayor of one of the district’s largest cities, would likely be the Democrat who could pull off that scenario.
However with other Democrats in the race, including state Reps. Marcus Hunter and Robert Johnson, the party would need to unite behind just one candidate for Mayo to be successful.
With a low turnout predicted for the contest, operatives say anything can happen on Saturday.
“Anybody that can successfully predict this special election should be a professional horse gamer,” one Republican said.
Rep. Elijah Cummings, D-Md., right, hugs Harold Schaitberger, General President of the International Association of Fire Fighters, after the Congressman spoke at the IAFF's Legislative Conference General Session at the Hyatt Regency on Capitol Hill, March 9, 2015. The day featured addresses by members of Congress and Vice President Joe Biden.