Explainer - Why the winners in Georgia runoffs might not be known for days

FILE PHOTO: Republican U.S Senators David Perdue (top L) and Kelly Loeffler (bottom L) and their Georgia runoff election challengers, Democratic U.S. Senate candidates Jon Ossoff and Rev. Raphael Warnock, are seen in a combination of file photos. REUTERS/Staff/File Photo

(Reuters) - The future of Democrat President-elect Joe Biden's agenda hinges on two Senate runoff races in Georgia whose outcome might not be known for days after polls close on Tuesday.

Public opinion polls show Republican incumbents Kelly Loeffler and David Perdue have about the same level of support as their Democratic challengers Raphael Warnock and Jon Ossoff.