The balance of power in the Senate may not be decided until weeks after Election Day.
Republicans need six more seats to win a majority. If they clinch fewer than that by the end of Tuesday, all eyes will turn to Louisiana and Georgia, where polling suggests the tight races could need runoffs.
In both states, the winning candidate must attract more than 50 percent of the vote to avoid a run-off.
In Louisiana, most polls have shown neither Democrat Sen. Mary Landrieu nor Republican Rep. Bill Cassidy clearing that threshold. Cassidy averages roughly 49 percent, while Landrieu scores about 44 percent in a head-to-head match-up, but a third candidate, Rob Maness, is drawing about 15 percent of the vote when he is included in polling.
Likewise in Georgia, Republican David Perdue is averaging 47 percent, with Democrat Michelle Nunn at 44 percent, according to Real Clear Politics.
Louisiana would hold a run-off if necessary on Dec. 6, while Georgia would wait until Jan. 6, 2015 — three days after the new Congress is sworn in.
Democrats would still face stiff odds in either runoff. Both states historically favor Republicans, and Democrats’ hopes have hinged largely on turning out a higher share of African American voters than is normal for a midterm election.
Landrieu attempted to appeal directly to black voters in a recent iNBC News interview, saying, “I’ll be very, very honest with you. The South has not always been the friendliest place for African-Americans. It’s been a difficult time for the president to present himself in a very positive light as a leader.”
Outside groups are already preparing for a long fight. Freedom Partners Action Fund, a group under the Koch umbrella, has reportedly reserved $580,000 for a Georgia Senate runoff and another $1 million in Louisiana. The National Republican Senatorial Committee and a handful of other pro-Republican groups have also reserved ad time in Louisiana.
Should the Senate hang in the balance, the races could attract tens of millions of dollars in additional spending.
