As voters prepare to head to the polls and the number of Americans casting early ballots surges, election analysts will likely focus on one question: Will the Democratic "blue wave" be powerful enough to reverse the early leads wracked up by Republicans in seven out of eight key battleground states? 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.

But in what may be an ominous sign for the left, while Democrats are boasting a narrow lead over Republicans nationally, Republicans are leading in the key swing states, including Arizona and Florida. Still, this comes with an important caveat: Early voting data can only show who voted, not for whom they voted.

There are other notable orthodoxies that may or may not hold:

Midterm elections tend to have two notable trends: the incumbent president’s party almost always loses seats, and Republicans tend to turn out more than Democrats. This year, those two forces collide. "It’s a real open question as to what ultimately that enthusiasm gap turns out to be," said Kathryn Pearson, a professor at the University of Minnesota.

At the center of this issue is an important question: Are these new voters who haven't turned out in past elections? Or simply people shifting the timing of their vote? There are some signs that the former scenario might be closer to reality.

According to Bloomberg, analysts will be looking at places like suburban Minnesota as bellwethers for Republican prospects:

Two good signs for Democrats: Women are voting at a much higher level than men in early voting, according to The Hill’s Reid Wilson, and turnout among voters aged 18-29 (who historically don’t vote at nearly the level of older voters) is way up in swing states - more than 400% in Georgia and Texas and more than 700% in Tennessee. In Nevada, political sage Jon Ralston says he thinks Democrats have banked enough of an early vote edge (23,000 votes statewide) that Senate challenger Jacky Rosen has an edge on Republican incumbent Dean Heller. In the Texas Senate race, both candidates - Republican incumbent Ted Cruz and Democratic Representative Beto O’Rourke - say the high turnout will benefit their campaigns. "We’re getting general confirmation where we can get data that the polls are correct that we have some very close Senate and gubernatorial races out there. The early vote looks very close," McDonald said. "Maybe in Florida things are a bit closer than what the polls suggest,” including in the governor’s race where Democrat Andrew Gillum has had a slim but persistent lead in the polls over Republican Ron DeSantis. How then to read the tea leaves? "I would go with the high turnout model at this point, I think that’s a safe assumption," McDonald said. "We are not seeing a 2014 election, we’re seeing a cross between a midterm and a presidential election."

The uncertainty among the professional forecasting class, which is still stinging from their embarrassingly wrong predictions in the 2016 presidential vote and the Brexit vote, 538's Nate Silver said that, while his models project Democrats have a 80% chance of retaking the House, in reality, the odds may be closer to 50-50.

"The range of outcomes in the House is really wide," he explained. "Our range, which covers 80 percent of outcomes goes from, on the low end, about 15 Democratic pickups, all the way to low to mid 50s, 52 or 53." "Most of those are under 23, which is how many seats they would need to win to take the House," he said." "But no one should be surprised if they only win 19 seats and no one should be surprised if they win 51 seats," Silver added. "Those are both extremely possible, based on how accurate polls are in the real world."

For what it's worth, Wall Street and the business community, which typically lean Republican, is hedging its bets and contributing more dollars to Democrats this year, giving $85 million to Dems, compared with $76 million to the GOP this year, as of Oct. 17, in what is projected to be the most expensive midterm election in US history, with some $5 billion expected to be spent in total.