Republicans need to pick up six seats to take control of the chamber. Anything less would result either in a tie or Democratic control, and Vice President Joe Biden could always break a perfect split. If King switched to the GOP, though, that could move the balance as well.
A King spokesman said the senator's statement was consistent with what he's previously said on how he plans to serve as a senator.
"Sen. King only told The Hill newspaper what he’s always said – that his guiding principle is, and always will be, to do what is right for Maine," the spokesman said in a statement. "He's a proven consensus builder and will continue to work with members on both sides of the aisle, regardless of who’s in charge. He believes the people of Maine sent him here to find solutions and that's all he's focused on."
Reached by TPM, Democratic leadership strongly cast doubt that King would start caucusing with Republicans.
Forecasting guru Nate Silver recently projected that Republicans have a 60 percent chance of winning six Senate seats and taking control of the chamber. But in his assessment Silver cautioned that that depends on a number of factors.
"The balance has shifted slightly toward the GOP," Silver wrote. "But it wouldn’t take much for it to revert to the Democrats, nor for this year to develop into a Republican rout along the lines of 2010."
This post was updated.