Because the Republicans are in control of both the US Senate and House of Representatives, the Midterms have been framed as the ruling party playing defence. The GOP vows that the Democratic 'Blue Wave' will meet a Republican 'Red Wall'.
So the Democrats need 23 House seats for a majority. The Cook Political Report rates 30 Republican-held seats as "toss-ups".
FiveThirtyEight's final forecast of odds is:
• A 68 per cent chance of a Republican Senate and a Democrat House
• An 18 per cent chance of a Democrat Senate and a Democrat House
• A 14 per cent chance of a Republican Senate and a Republican House
• A 1 per cent chance of a Democrat Senate and a Republican House.
A final Gallup poll today shows the Democrats up by 11 - 54 to 43 per cent - in the generic ballot ('do you want a Democrat or Republican') among likely voters. Most polls have shown the gap at about seven or eight points.
We know there's been major enthusiasm for early voting, but it's unclear what that really means. Early voting appears to be up across voter groups.
As part of the analysis on US elections voters get sliced and diced into categories. Certain groupings can reliably be sorted into Republican or Democrat columns. African-Americans and Hispanics, for instance, are key members of the Democratic base. Other voter groups float more between the parties.
We know that polls consistently show a gender chasm. Women generally favour Democrats markedly over Republicans whereas for men it's tighter, with Republicans favoured.
When it comes to party affiliation, most voters - 39 per cent - classify themselves as independents at present, according to Gallup's most recent survey in early October. Democrats make up 30 per cent and Republicans 28 per cent.
While Trump is not up for election, today we will learn a lot more about where Trumpism is at now, two years on.
The very first results, from Kentucky at Noon NZT, will give us clues as to where we are headed.
It's a Lexington House district in a conservative state which Trump won by double digits.
Third-term Republican Congressman Andy Barr is battling one of the Democrats' impressive female candidates Amy McGrath, a retired Marine fighter pilot.
A lot of the race is taking part on Republican-held soil, but Democrats see openings in urban, suburban areas. Trump's approval ratings nationally have been consistently low for a new president running a well-performing economy.
In the 2016 presidential election 137.5 million people voted, a turnout of 61.4 per cent of those eligible. Whites made up 73.3 per cent of voters in 2016 and minority voters 26.7 per cent.
Those figures show the majority clout of the white section of the electorate, though it has fallen from 85 per cent in 1988.
A lot of media attention has focused on Trump's attempts to get the best Midterms turnout he can out of his core base - whites without a college degree (as they are referred to in the polls).
Back in the 1980s, white working-class voters - a traditional section of the Democratic Party - were lured to the opposition by Ronald Reagan and became known as Reagan Democrats. But both Bill Clinton and Barack Obama were able to later forge coalitions of enough white voters and minority supporters to win two-term presidencies.
Census data determined that of the six states that shifted from Obama to Trump in 2016 – Florida, Iowa, Michigan, Ohio, Pennsylvania and Wisconsin – only in Florida was there actually an increase, of about 3 per cent, in white working-class turnout.
The Washington Post reported that white working-class turnout was virtually the same as the previous presidential cycle. Trump was able to draw 66 per cent of those that did vote, compared to 61 per cent who voted for Mitt Romney in 2012.
Trump won 58 per cent of the white vote overall compared to Romney's 59 per cent. On the Democrat side, Hillary Clinton drew 37 per cent of whites, down from Obama's 39 per cent, according to the 2016 exit poll.
Clinton was hurt far more by an election-wide depression in African-American turnout – down 7 per cent on 2012 – and flat Hispanic turnout. Not to mention non-voting and third-party voting.
In the Midterms, the Democrats are hoping to attract independents and higher educated suburban Republicans, who might be turned off by Trump's anti-immigration rhetoric.
An NBC/Wall Street Journal poll on Monday showed that Democrats were favoured by whites with a college degree (56 per cent) and women overall (55 per cent). At the same time whites with no college degree preferred Republicans by 60 per cent. Bear in mind that Trump attracted 66 per cent of that group two years ago.
Writing in New York Mag, Gabriel Debenedetti, says Democrats have made inroads across the Midwest with electorates concerned about healthcare, education funding and, tariffs.
In a Pennsylvania special election in March, "the results didn't show a flood of blue-collar men coming back to the Democratic fold, but rather a crumbling of GOP support in the suburbs matched by a lack of energy among … first-time Republican-voting Trump supporters".
All these theories will now be put to the test.
