
Americans headed to the polls on Turesday in crucial midterm elections that will serve as a referendum on the first two years of President Donald Trump's presidency and determine how much – or how little – help he will have in Congress during the rest of his first term.

Every seat in the House of Representatives is up for grabs, along with 35 of the 100 Senate seats. Voters will also decide on 36 races for state governors.

Republicans aim to hold their majorities in both chambers of Congress. Democrats are trying to take over in what pundits call a 'blue wave.' Trump will gather with friends and family to watch the results in the White House, according to Press Secretary Sarah Sanders.

With Trump as president, the nation's off-year political contests have taken on the character of the World Series instead of the sleepy minor-league affairs they usually are.

Campaigns spent more than $3.27 billion on TV and radio ads alone, and another $900 million in online ads, according to Kantar Media/CMAG, which tracks those numbers.

A shift of just 23 seats would put the House in Democrats' hands and likely install the long-suffering Nancy Pelosi, 78, as speaker. Most forecasters consider that outcome likely but not guaranteed.

If they're right, control of the chamber woud switch hands for the third time in 12 years. America hasn't seen that level of fluctuation since World War II.

In the Senate the margin is narrower: A swing of just two seats would cost Republicans their gavel. But the realities of America's electol map make it a harder task than flipping the House.

JUDGMENT DAY: Virginia Democratic congressional candidate Jennifer Wexton greeted voters Tuesday morning in the town of Leesburg as she tries to unseat a two-term Republican congresswoman; the hotly anticipated midterm elections will determine the governing environment in which President Donald Trump must function for the next two years

Trump faces a referendum on his first two years in office and could end up anywhere from complete victory to total defeat

Voters lined up early on Tuesday in Doylestown, Pennsylvania as the age of Trump has given new significance to what might otherwise have been a sleepy off-year election cycle

All 435 seats in the House of Representatives are on ballots, with most polls forecasting that Democrats will take control from the Republicans

In the Senate the Democrats are facing an uphill battle because just 35 of the 100 seats are up for election, and they have to defend the majority of those as incumbents

Democrats are defending 26 of the 35 contested Senate seats. Ten of those are in states Trump won by wide margins in 2016.

Of the nine Republican incumbents trying to save their jobs, four are considered safe.

At stake is the future of the populist political movement that sent Trump to Washington: A win for Republicans would quash his critics inside the GOP and embolden him for at least two more years of pro-business, 'America First' governing that's hawkish on trade and uncompromising toward illegal immigration.

But a Democratic House could cripple his legislative agenda and dring the wheels of government to a halt as his political enemies launch investigations into allegations of election-year collusion with Russia and a growing list of other scandal-ready material.

If the Senate should go 'blue,' Trump would lose the practical ability to appoint more federal judges – including Supreme Court justices – and replacements for cabinet members who are likely to walk away after two years in office.

Should Democrats win control of both chambers of Congress, an impeachment mood would sweep Washington, forcing the White House to play constant defense until 2020.

The president hinted on Monday that he senses the possibility of a quiet voter revolt that pollsters can't measure, similar to the one that sent him to Washington two years ago.

He said at allthree of his final campaign day's rallies that Republicans might shock the world again no matter what the political press corps predicts.

'There is something going on, Ohio, that they’re not talking about,' he said in Cleveland after greeting about 6,000 people in a sea of red hats.

'There’s an electricity like people have not seen since a date in 2016. November,’ Trump said, adding later that 'we defied the pundits and the critics. We rejected them.'

He also took credit for the resurgence of the midterm elections as a media phenomenon.

'You know the midterm elections used to be, like, boring, didn't they?' he asked his screaming fans. 'Do you even remember what they were? People say midterms, they say, "What is that? What is it?" right? Now it's like the hottest thing.'

Trump appeared Monday in three separate states for rallies, making his final sales pitch in Cape Girardeau, Missouri and sharing the stage briefly with press secretary Sarah huckabee Sanders

Rep. Beto O'Rourke, the 2018 Democratic Candidate for Senate in Texas, left his polling place with his family after voting on Tuesday

At stake on Tuesday is the future of the populist political movement that sent Trump to Washington

The U.S. flag flew in a dawn breeze on top of the White House as misty rain fell on Tuesday

Maricopa County, Arizona election officials expected huge crowds on Tuesday; official Deborah Atkins placed a bilingual 'vote' sign outside a polling place before sunrise in Phoenix

One closely-watched race is in Texas, where Republican Ted Cruz - who fought Trump for the presidency in 2016 - has been dragged into a close contest with Demorcatic congressman Beto O'Rourke

O'Rourke has emerged from relative obscurity to embody a Democrat party that hopes to galvanize the young and reach beyond its base into America's heartland

Trump has thrown his weight behind efforts to hold the Senate, engaging in a whirlwind series of rallies that saw him stumping in 11 cities over five straight days.

His late efforts might be wasted in portions of 37 states and the District of Columbia, however, where voters can cast their ballots early.

At least 36 million Americans voted before Election Day, many of them before the president engaged at full-throttle.

Trump downplayed that Monday in Ohio, suggesting that it won't be any more of a factor than it was in 2016.

'I remember they said, "Well, the people are sort of holding for Tuesday",' he said, recalling his victory two years ago. 'And did you show up on Tuesday!'

Trump hit the road in the past week to address crowds in battleground states of Ohio, West Virginia, Indiana, Montana, Florida and Missouri.

He has also addressed the faithful in Tennessee, where GOP Senate hopeful Marsha Blackburn is locked in a close race to replace a retiring Republican – and in Georgia, where a black woman could become a state governor for the first time in American history.

Voting in Tennessee will be a test of Trump's appeal because of how closely Blackburn has allied herself with both the man and his policies.

Missouri is another tight Senate race to watch, with Democratic incumbent Claire McCaskill running neck-and-neck against Republican state attorney general Josh Hawley.

McCaskill has opened up a small lead in one poll while Hawley edges her in another.

In Florida a close contest for the governor's seat is taking place between Andrew Gillum (left) and Ron DeSantis (right), who is a close ally of Trump

The President's job personal approval rating ranges from 42 to 51 per cent nationally, and polls show an even wider swing in voters' party preference going into Tuesday's contests.

A CNN poll released Monday morning had Democrats leading Republicans by 13 percentage points when voters were asked which party's candidate they were likely to support in a congressional race.

A Politico poll released at the same time showed that gap was just 3 points, in a survey with a 2-point margin of error.

Texas is another state that has landed itself on the Democrat list of targets despite no member of their party holding a Senate seat there since 1994.

Sen. Ted Cruz, who fought a bitter contest with Trump during the 2016 election but has since warmed to him, is fendingoff a challenge from Democratic congressman Beto O'Rourke.

O'Rourke has come to represent what many Democrats hope will be the new face of their party – a young, firey liberal who captured young Tecans' imagination while raising extraordinary amounts of money through small donations.

While polls have Cruz leading by an average of 6.6 points, his seat was considered 'solid red' until O'Rourke arrived and created a contentious race out of it.

Two governor's races have also captured the attention of the nation in what have become bitter contests with race a central theme.

Stacey Abrams is looking to become the first female African American governor in US history in Georgia, where she is taking on Brian Kemp

Kemp, another close ally of Trump, is locked in a neck-and-neck tie with Abrams amid allegations of racism and voter suppression

In Georgia, Republican Brian Kemp and Democrat Stacey Abrams are battling it out in a race which remains too close to call, and could drag on until next month.

With a third candidate also in the running, the two top finishers would advance to a runoff in December if no one wins more than half the votes.

Kemp is a staunch ally of Trump who has rallied for his man and declared Abrams 'one of the most extreme far-left politicians in the entire country.'

Meanwhile Abrams has attracted endorsements from Oprah Winfrey, Barack Obama and Will Ferrell.

During the campaign she has been targeted by racist robocalls mimicking Oprah's voice and asking people to vote for Kemp.

In Florida, Democrat Andrew Gillum is battling Republican Ron DeSantis for the governorship. Gillum is the black mayor of Tallahassee, the state's capital. His record presiding over the crime-infested mini-metropolis has made him a ripe target for Trump and other Republicans.

Gillum, who polls suggest is leading by four points, has painted his opponent as pandering to racists and the far right.

Meanwhile DeSantis has borrowed from Trump's playbook by focusing on illegal immigration and jobs, while also trying to paint Gillum as corrupt.