What to watch

The timeline

Polls start closing at midday NZT in Kentucky. But things will really get rolling at 1pm, when polls close in Georgia, Indiana, Kentucky, South Carolina and Virginia. Another wave of numbers will begin coming in after 1.30pm from North Carolina, Ohio and West Virginia. A big chunk of data will come after 2pm and 3pm when states such as Texas, New York, Michigan and Pennsylvania begin reporting. The 5pm batch of states includes California, home to several competitive congressional races. Alaska, where polls close at 7pm, will end the day.

The early vote

Much of America had already voted before today. Based on reports from 49 states through to yesterday, at least 36.4 million people voted in the Midterms before Election Day. And in a sign of the growing influence of early voting, 30 states reported exceeding their total number of mail and in-person votes cast ahead of the 2014 midterm elections.

A big question: Does it mean a higher turnout?

Turnout in Midterm elections is typically near 40 per cent, much lower than presidential elections, where turnout has hit around 60 per cent in recent cycles. University of Florida professor Michael McDonald, who studies voting patterns, estimated recently that about 45 per cent of eligible voters could cast ballots this year, a turnout level that hasn't been seen in nearly a half century.

Early tea leaves

For an early read on how things are going, keep an eye on two congressional races in Virginia: A district in the Washington suburbs represented by Republican Representative Barbara Comstock and another in the Richmond area held by Republican Representative Dave Brat.

Trump has struggled with college-educated women in the suburbs and Comstock's district

could be among the first casualties as she faces Democrat Jennifer Wexton. Brat, meanwhile, won his seat by upsetting then-House Majority Leader Eric Cantor in the 2014 GOP primary. But this time he is facing a serious threat from Democrat Abigail Spanberger, a former CIA officer.

Another district to watch is in Kentucky — the Lexington-area battle pitting third-term Republican Representative Andy Barr against Democrat Amy McGrath, a retired Marine fighter pilot. Trump won the 6th District by more than 15 percentage points in 2016. But McGrath has pushed Barr to the edge with the help of sharp campaign ads that went viral.

House stakes

Republicans have had control of the House since the tea party helped sweep them into power in the 2010 Midterms. Nearly a decade later, the GOP is trying to avoid a “blue wave” that returns Nancy Pelosi and House Democrats to the majority.

Control of the House is expected to be determined by a few dozen districts, many of them in the nation's suburbs. Democrats need a net increase of 23 seats to win back control — a number that many GOP officials concede is a very possible outcome.

Senate stakes

Republicans hold a narrow Senate majority, 51-49, but have a huge advantage in these contests because the battle for control runs mostly through states that Trump won in 2016.

To put it simply: Democrats are on defence. Of the 35 Senate races, 10 involve Democratic incumbents seeking re-election in states won by Trump, often by large margins. Democrats' hopes of recapturing the Senate hinge on all their incumbents winning — a difficult task — and on flipping seats in Nevada, won by Hillary Clinton in 2016, and a few states that lean Republican, most notably Arizona, Tennessee and Texas.

Another epic clash to watch: A race involving Texas Senator Ted Cruz, Trump's one-time GOP presidential rival, against Democratic Representative Beto O'Rourke.