Many have spent the past few weeks vigorously campaigning in Iowa, which is always the first to vote. The primaries contest goes on until early June, and moves on to New Hampshire next Tuesday.
Polls suggest that Bernie Sanders has risen to be the favorite in Iowa.
He is one of four senators running for president who have had to stay behind in Washington to attend President Trump’s impeachment trial, but his supporters, including Alexandria Ocasio-Cortez, a well-known congresswoman, have been energetically campaigning on his behalf in Iowa.
Four years after losing out to Hillary Clinton, the 78-year-old is now backed by a huge pot of donations and a team of hundreds.
Some of the other big names including Elizabeth Warren, Amy Klobuchar and Pete Buttigieg will be hoping Bernie Sanders doesn’t have it all his own way in Iowa.
There are also Republican caucuses on February 3, and two people are running against Donald Trump, but the president’s popularity within his own party is such that his nomination is all but a formality.
Iowa, to some extent, provides a glimpse of what went wrong for Democrats in 2016.
In the last election, more than 200 counties flipped from supporting President Barack Obama in 2012 to backing Donald Trump – and 31 of those counties were in Iowa.
Democrats will be hoping to lure back those swing voters in 2020.
Howard County in northern Iowa flipped by 41 percentage points in 2016, the largest change in the US.
Former South Carolina Mark Sanford has become the latest Republican to challenge President Donald Trump in the GOP’s primary contest.
Mark Sanford, a long-time Trump critic, said in an interview announcing his candidacy: “I’m here to tell you now that I am going to get in.”
The former governor is the third person to challenge Donald Trump for the nomination.
However, it is seen as near impossible that anyone will take the Republican mantle from the president. No sitting president in the modern era has lost the race to be nominee for their own party, and Donald Trump remains very popular with Republicans.
The Republican National Convention, at which the nominee will be formally chosen, will take place in late August 2020 after a series of state primary elections and party caucuses.
However, some state Republican parties, including in South Carolina, have decided not to hold primaries in 2020 – to clear the path for Donald Trump and save money.
Mark Sanford, 59, is expected to centre his campaign on cutting government debt and spending.
He told Fox News on September 8: “I think we need to have a conversation on what it means to be a Republican. I think that as a Republican party we have lost our way.
“We have lost our way on debts and deficits and spending… The president has called himself the king of debt, has a familiarity and comfort level with debt that I think is ultimately leading us in the wrong direction.”
In April, former Massachusetts Governor Bill Weld became the first person to challenge Donald Trump.
Bill Weld was followed by conservative radio host and former lawmaker Joe Walsh at the end of August.
Mark Sanford first served in Congress in 1995, representing South Carolina’s first congressional district. He later served as the state’s governor for two terms from 2003-2011. He then returned to the House in 2013.
The former governor criticized Donald Trump during the 2016 presidential election but ultimately supported him. However, Mark Sanford would become one of his toughest Republican critics in Congress when President Trump took office.
That stance cost Mark Sanford the Republican primary when his seat was up for re-election last year. He was beaten by a pro-Trump challenger who went on to lose the election to her Democrat opponent.
Mark Sanford is known as a fiscal conservative and has been attacked by President Trump over an extra-marital affair that tainted his second term as governor.
He went missing for several days, with his staff telling reporters he had gone to hike the Appalachian Trail.
Mark Sanford later admitted he had instead gone to Argentina to see his mistress.
Election Day is still more than a year away but the race to become the Democratic challenger to President Trump is already well under way.
Bernie Sanders and Joe Biden have thrown their hats into the ring, but most of the other candidates are relatively unknown outside the Washington DC bubble.
During his roughly 80-minute speech, President Trump reiterated key themes of his winning 2016 campaign.
The president pledged to continue a crackdown against illegal immigration, one day after tweeting that US Immigration and Customs Enforcement (ICE) would soon begin removing “millions of illegal aliens” from the country.
He told Florida supporters: “We believe our country should be a sanctuary for law-abiding citizens, not for criminal aliens.”
Donald Trump also accused Democrats of seeking to legalize illegal immigration in order to boost their voting base, and said they “want to destroy our country as we know it”.
President Trump described his opponents as a “radical left-wing mob” who he said would bring socialism to the US.
He told the crowd: “A vote for any Democrat in 2020 is a vote for the rise of radical socialism and the destruction of the American dream.”
President Trump also praised the economy, criticized the Mueller investigation into alleged collusion between the 2016 Trump campaign and Russia, and referred to media covering the event as “fake news back there”.
Donald Trump also elicited “lock her up” chants from supporters when he brought up Hillary Clinton, despite her not being in the 2020 race.