Voters across America are going to the polls today for the midterm elections. 

All 435 seats in the House of Representatives are up for grabs, as well as 35 Senate seats.

Voters will also cast ballots in 36 governor races and many local and state elections.

One person who is not on the ballot today is US President Donald Trump, but the vote will be seen as a referendum on his presidency.

The outcome will have big implications for the remaining two years of his first term.

Traditionally, the party of the sitting US president loses seats in Congress in the midterm elections.

With President Trump's low approval ratings, Democrats are hopeful and are predicting a "blue wave" of support.

Pollsters say Democrats are in with a good chance of winning control of the House of Representatives.

They need to claim an additional 23 seats, which most analysts agree is achievable. The Senate is a different matter.

Republicans hold the slimmest of majorities there but most of the Senate seats up for grabs are already held by Democrats and they may struggle to retain all of them.

President Trump will breathe a sigh of relief if his party maintains its majority in the Senate, but losing control of the House of Representatives could create big problems for him.

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David Hopkins is a professor of political science at Boston College. He says that if the Democrats win control of the House, it will mean a lot of partisan fighting when it comes to President Trump trying to advance his legislative agenda.

"It will also mean that the Democrats will have the power to conduct oversight and investigations of the Trump presidency, his campaign, and the man himself, in a way that may end up being politically damaging for the president," he said.

Committee hearings and investigations could become very common under a Democrat-controlled House and, according to Professor Hopkins "there could be lots of inconvenient facts that might come to light from congressional investigations of the 2016 Trump campaign or the last two years of the Trump administration".

Read more:

Poles apart: A guide to the US midterms
The view from the 'rust belt'
Taking a gamble - The view from Las Vegas
In the shadow of the Alamo, another battle for Texas

The stakes are high for the US President and he has hit the campaign trail hard. In recent weeks, he returned to familiar ground, addressing crowds of cheering supporters.

He has been criss-crossing the country, sometimes holding two or three rallies a day.

He has been working hard to get out the vote among his support base, but rather than focusing on the strong US economy, he has decided to make immigration his central campaign message.

President Trump has repeatedly referred in his speeches to the caravan of migrants making its way through Central America towards the US border.

He claims that when it comes to illegal immigration and border security, Republicans are strong and Democrats are weak.

It is a tactic that may be having some impact. Democrats were still ahead in the polls going into today's vote, but the gap had narrowed in recent days.

There are record numbers of women and ethnic minorities running for office, but traditionally voters in midterm elections tend to be white, older and conservative.

If Democrats are to do well, turnout will be key and they will need to mobilise their base in the same way Mr Trump rallied support two years ago.

Otherwise, we will not be talking about a "blue wave" tomorrow, rather it will be a case of a "red rally".