United States Senator Bernie Sanders raised more than $34.5m in the last quarter of 2019, the largest three-month haul for a 2020 Democratic presidential candidate, while Republican President Donald Trump drew $46m on the heels of his impeachment, their campaigns said on Thursday.

The new figures brought Sanders's total campaign fundraising last year to $96m, making him the leading fundraiser so far among 14 Democrats vying to face Trump in November's presidential election. States begin choosing candidates next month with the Iowa caucuses on February 3.

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Trump, a polarising president popular with a large majority of Republicans but vilified by many Democrats, maintained his formidable fundraising edge over Democrats with a surge of donations following his impeachment last month by the US Congress's Democratic-led House of Representatives.

"Democrats and the media have been in a sham impeachment frenzy and the president's campaign only got bigger and stronger with our best fundraising quarter this cycle," Trump's campaign manager, Brad Parscale, said in a statement. Trump was impeached for obstruction of Congress and abuse of power over his dealings with Ukraine. He is expected to be acquitted in a Senate trial this month.

The Trump campaign's latest quarter eclipsed a third-quarter fundraising haul of nearly $41m. It begins the 2020 re-election year with cash on hand of $102.7m, it said - an amount that will help Trump's bid to compete in states beyond those that carried him to a surprise victory in 2016.

Trump speaks during a Keep America Great rally at Kellogg Arena in Battle Creek, Michigan [File: Je Kowalsky/AFP]

Some Democrats have not yet disclosed their fourth-quarter fundraising numbers, but those who did had strong showings.

Former Vice President Joe Biden said on Twitter that his campaign raised $22.7m in the last three months of 2019, the biggest quarter of the campaign so far.

Pete Buttigieg raised $24.7m in the fourth quarter, a hefty total expected to land him among the top fundraisers in the Democratic field. Businessman Andrew Yang raised $16.5m, well over the nearly $10m he took in previous quarter.

Senator Elizabeth Warren has not released her latest fundraising figures.

Warren's campaign told supporters last week that it needed more donations to meet its $20m goal for the quarter. Biden's fundraising lagged behind those of his main rivals in the last quarter.

'Grassroots movement'

Sanders, who wants to reduce the sway of corporate America and economic inequality, has built his campaign on small donations, largely through online fundraising from an ethnically diverse, mostly young coalition of supporters.

Campaign manager Faiz Shakir said Sanders's "grassroots movement" showed he was the best-placed candidate to defeat Trump.

"He is proving each and every day that working-class Americans are ready and willing to fully fund a campaign that stands up for them and takes on the biggest corporations and the wealthy," Shakir said in a statement.

Sanders, 78, bounced back from a heart attack in early October to win growing support for his platform of expanding government-run healthcare, making college free, and bolstering investment in renewable energy paid for with higher taxes on the wealthy.

Two billionaires in the Democratic race, Tom Steyer and Michael Bloomberg, are relying on their own money to fund their campaigns but have not released their latest funding figures.

Bloomberg has spent more than $76m on television ads since November 16, while Biden, Warren, Sanders and Buttigieg have spent a combined $13.2m all year, according to an analysis by the Wesleyan Media Project citing Kantar Media/CMAG political advertisement data.

Bloomberg, a New York media mogul who only entered the race in November, has outspent Steyer, who has put more than $72m into TV ads this year.

Bloomberg has risen to fourth place in the Democratic race with the support of about five percent of Democratic-leaning voters, according to a Reuters/Ipsos poll conducted December 18-19, while Steyer has just garnered two percent support.