So far, enthusiasm levels among both Democrats and Republicans have climbed to historic levels, complicating the efforts of forecasters and throwing the forecasting orthodoxy - the notion that Republicans will pick up Senate seats while Democrats wrest back control of the House - into doubt with the polls set to open across the US in 24 hours.

According to Bloomberg, some 34 million people have already voted in the 2018 midterms, and, in at least 28 states and the District of Columbia, early voter tallies have already surpassed their totals from the 2014 midterms.

In Texas alone, where Ted Cruz is defending his seat from Democratic challenger Beto O'Rourke, more than 4.5 million people have already voted. That momentum has apparently carried over from the record turnout during primaries and special elections this year. "People are engaged and voting in this election," said University of Florida professor Michael McDonald.