Whatever the outcome, the United States' 2018 midterm elections have already reached a milestone: record spending for any midterm polls to date at US$5.2 billion (S$7.2 billion).
Money is one measure of the stakes in tomorrow's midterms.
Another is turnout. While the final figure remains to be seen, the turnout for early voting was twice that of the last midterms in 2014 - a sign of how energised voters are.
By the weekend, 33.8 million Americans had already cast ballots, with the number of early voters in at least 28 states exceeding that in 2014.
Prior to this year's elections, no midterms have surpassed more than US$4.2 billion in spending when adjusted for inflation, said the Centre for Responsive Politics (CRP), a non-profit research group.
"The overall estimated cost of the 2018 elections would represent a 35 per cent increase over the 2014 cycle in nominal dollars, the largest increase in at least two decades," the group said on its Open Secrets website.
Republican candidates are raising funds at record levels, but the big surge is being fuelled by Democrats, who are projected to spend more than US$2.5 billion - topping Republicans, who are expected to spend roughly US$2.2 billion.
Democratic House candidates, in particular, have raised more than US$951 million, way ahead of their Republican opponents' US$637 million, CRP said. The gap is smaller in the Senate races.
Las Vegas billionaires Sheldon and Miriam Adelson have been the Republicans' biggest donors, shelling out more than US$113 million. The relatively lesser-known, Illinois-based shipping supplies billionaire Richard Uihlein and his wife Elizabeth have donated more than US$39 million.
On the opposite side, San Francisco-based billionaire hedge fund manager and environmentalist Tom Steyer has committed nearly US$51 million to the Democrats.
Billionaire and former New York City mayor Michael Bloomberg has so far contributed US$38 million.
The Democratic Party has also seen a surge of donations from women, the CRP reported.
Much of the money goes into television advertising - and mostly negative attack ads.
As of last week, Phoenix, Arizona, was the most saturated market, with more than 41,000 political spots aired on broadcast television between Sept 3 and Oct 16, reported USA Today.
Midterms normally see tepid turnout - only about 40 per cent of eligible voters after World War II. But this year's turnout has already shot up, though there is not necessarily any correlation with money spent.
Texas saw more than 4.5 million early voters, surpassing the entire turnout in the 2014 midterms. In the state's most closely watched race, Democratic congressman Beto O'Rourke is in a statistical tie in opinion polls with sitting Republican Senator Ted Cruz.
Mr O'Rourke has raised record amounts of cash, and analysts say that even if he does not win - the state has not elected a Democrat to the Senate in 20 years - the fact that he will have come close speaks volumes about energised Democrats just two years before the 2020 presidential election.