Donald Trump has boasted of beating the “Barack Hussein Obama dynasty”, telling a rally in Mississippi he was “kicking the ass” of his predecessor and his supporters.

At an event held almost precisely a year from 2020’s election day, Mr Trump unleashed a series of coarse and offensive comments that have increasingly become his trademark.

He dismissed the impeachment investigation being undertaken against him by Democrats as “crap”, and referred to former congressman Beto O’Rourke, who hours earlier had announced he was ending his bid to be the party’s 2020 presidential challenger, as a “poor b***ard”.

As Mr Trump was speaking in the city of Tupelo, the birthplace of Elvis Presley, and where he was appearing to support Republican Tate Reeves, who is locked in a tight race to become governor in a vote next week, Democrats met in Des Moines. At the Iowa Democratic Party’s Liberty and Justice Celebration, 14 hopefuls spoke for 10 minutes each, as they sought to make their case to take on Mr Trump next year.

The event, a bookmark in the political calendar for Democrats, has been the place many candidates have previously shone, including Mr Obama, who used a 2007 speech there to boost his campaign. The following year, he stunned many by winning the state and going on to seize the White House.

The Democrat challengers to Trump in 2020 Show all 25 1 /25 The Democrat challengers to Trump in 2020 The Democrat challengers to Trump in 2020 Bernie Sanders The Vermont senator has launched a second bid for president after losing out to Hilary Clinton in the 2016 Democratic primaries. He is running on a similar platform of democratic socialist reform Getty The Democrat challengers to Trump in 2020 Joe Biden The former vice president recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well and has since maintained a front runner status in national polling EPA The Democrat challengers to Trump in 2020 Elizabeth Warren The Massachusetts senator is a progressive Democrat, and a major supporter of regulating Wall Street Reuters The Democrat challengers to Trump in 2020 Amy Klobuchar Klobuchar is a Minnesota senator who earned praise for her contribution to the Brett Kavanaugh hearings Getty The Democrat challengers to Trump in 2020 Michael Bloomberg Michael Bloomberg, a late addition to the 2020 race, announced his candidacy after months of speculation in November. He has launched a massive ad-buying campaign and issued an apology for the controversial "stop and frisk" programme that adversely impacted minority communities in New York City when he was mayor Getty Images The Democrat challengers to Trump in 2020 Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but has faced tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Pete Buttigieg The centrist Indiana mayor and war veteran would be the first openly LGBT+ president in American history Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Deval Patrick The former Massachusetts governor launched a late 2020 candidacy and received very little reception. With just a few short months until the first voters flock to the polls, the former governor is running as a centrist and believes he can unite the party's various voting blocs AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Beto O'Rourke The former Texas congressman formally launched his bid for the presidency in March. He ran on a progressive platform, stating that the US is driven by "gross differences in opportunity and outcome" AP The Democrat challengers to Trump in 2020 DROPPED OUT: Kamala Harris The former California attorney general was introduced to the national stage during Jeff Sessions’ testimony. She has endorsed Medicare-for-all and proposed a major tax-credit for the middle class AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Bill De Blasio The New York mayor announced his bid on 16 May 2019. He emerged in 2013 as a leading voice in the left wing of his party but struggled to build a national profile and has suffered a number of political setbacks in his time as mayor AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Steve Bullock The Montana governor announced his bid on 14 May. He stated "We need to defeat Donald Trump in 2020 and defeat the corrupt system that lets campaign money drown out the people's voice, so we can finally make good on the promise of a fair shot for everyone." He also highlighted the fact that he won the governor's seat in a red [Republican] state Reuters The Democrat challengers to Trump in 2020 DROPPED OUT: Cory Booker The New Jersey Senator has focused on restoring kindness and civility in American politics throughout his campaign, though he has failed to secure the same level of support and fundraising as several other senators running for the White House in 2020 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Wayne Messam Mayor of the city of Miramar in the Miami metropolitan area, Wayne Messam said he intended to run on a progressive platform against the "broken" federal government. He favours gun regulations and was a signatory to a letter from some 400 mayors condemning President Trump's withdrawal from the Paris Climate Accord Vice News The Democrat challengers to Trump in 2020 DROPPED OUT: Kirsten Gillibrand The New York Senator formally announced her presidential bid in January, saying that “healthcare should be a right, not a privilege” Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Delaney The Maryland congressman was the first to launch his bid for presidency, making the announcement in 2017 AP The Democrat challengers to Trump in 2020 DROPPED OUT: Andrew Yang The entrepreneur announced his presidential candidacy by pledging that he would introduce a universal basic income of $1,000 a month to every American over the age of 18 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Julian Castro The former San Antonio mayor announced his candidacy in January and said that his running has a “special meaning” for the Latino community in the US Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Marianne Williamson The author and spiritual adviser has announced her intention to run for president. She had previously run for congress as an independent in 2014 but was unsuccessful Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Eric Swalwell One of the younger candidates, Swalwell has served on multiple committees in the House of Representatives. He intended to make gun control central to his campaign but dropped out after his team said it was clear there was no path to victory Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Seth Moulton A Massachusetts congressman, Moulton is a former US soldier who is best known for trying to stop Nancy Pelosi from becoming speaker of the house. He dropped out of the race after not polling well in key states Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Jay Inslee Inslee has been governor of Washington since 2013. His bid was centred around climate change AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Hickenlooper The former governor of Colorado aimed to sell himself as an effective leader who was open to compromise, but failed to make a splash on the national stage Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tim Ryan Ohio representative Tim Ryan ran on a campaign that hinged on his working class roots, though his messaging did not appear to resonate with voters Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tom Steyer Democratic presidential hopeful billionaire and philanthropist Tom Steyer is a longtime Democratic donor AFP/Getty

On Friday, Mr Trump, who has previously questioned Mr Obama’s citizenship, launched new attacks on the 44th president. Using his full name and stressing Mr Obama’s middle name “Hussein”, he claimed he had defeated the “the Clinton dynasty, the Bush dynasty, the president Barack Hussein Obama dynasty”.

As the crowd booed, he added: “The only time I saw Barack Obama work hard is when he was trying to beat me”.

Mr Trump, who dismissed the impeachment investigation against him as a “witch hunt” and also insulted the media – such elements have become a staple of his speeches – found time to attack Joe Biden, one of the Democrats’ frontrunners to take him on in 2020.

Donald Trump calls Chicago 'embarassing'

At one point, Mr Trump mockingly impersonated the former vice president and claimed: “They’ve been plotting to overthrow the election since the moment I won.”

Mr Trump made clearly false claims about Democrat Jim Hood, who is challenging to become governor, calling him a progressive liberal. In reality, Mr Hood, the only statewide Democrat in Mississippi and who currently serves as its attorney general, is among the most conservative Democrats in the country.

He has previously said he would have signed the state’s new “heartbeat abortion law” had he been governor.

The event came a day after Democrats voted to formalise the investigation into whether Mr Trump abused his office and compromised national security when he asked the president of Ukraine to investigate one of his political rivals.

Aggrieved and feeding off the energy of the crowd, Mr Trump angrily defended himself against what he called the “deranged impeachment witch hunt” and accused Democrats of doing anything to take him down and invalidate the results of the 2016 campaign.

He said: ”While we’re creating jobs and killing terrorists, the Democrat Party has gone completely insane.“

The rally is one of a handful of events Mr Trump and vice president Mike Pence will be holding in the coming days to try to bolster Republican candidates running in gubernatorial elections.

Mr Trump is scheduled to travel to Kentucky on Monday to campaign for incumbent Matt Bevin. He is heading to Louisiana on Wednesday to campaign for Republican gubernatorial candidate Eddie Rispone, who is trying to unseat incumbent Democratic governor John Bel Edwards.