WASHINGTON (AFP) - America on Sunday (Nov 3) kicks off the one-year countdown to Election Day 2020, with President Donald Trump betting that an "angry" Republican surge can deliver him a second term, as the Democratic battle to win back the White House heats up.

The building political clash - dramatically fuelled by the House of Representatives' impeachment inquiry into Mr Trump - appears to virtually guarantee another year of sharp division in a nation long weary of such drama.

Polls suggest that the country could not be much more divided.

The latest projection from a University of Virginia political science team points to a dead-even 2020 race, with each party leading in states totalling 248 electoral college votes, 22 short of the 270 needed for election.

The division is reflected in the House, where the vote last Thursday to formalise the impeachment inquiry passed almost entirely on party lines - more partisan than any of the three previous impeachment votes in US history.

As that inquiry proceeds, Mr Trump has lashed out in increasingly angry, personal and crude terms, seeking to damage his political foes while energising a fiercely loyal base.

In a speech last Friday in Tupelo, Mississippi, he called Democratic leaders "mentally violent", denounced the impeachment inquiry as a "hoax" and said former vice-president Joe Biden, once a Democratic frontrunner, was getting "slower and slower".

Mr Trump has even retweeted, with apparent approval, a warning by an evangelical pastor that his impeachment could "cause a Civil War like fracture in this Nation".

Amid all the furore, the top Democratic candidates have struggled for a share of the spotlight while anxiety grows among some in the party that a clear, strong challenger with mainstream appeal has yet to emerge.

Mr Trump's focus on Mr Biden - and the allegations, for which there is no evidence, that he and his son were somehow tainted by corruption in Ukraine - has weighed on the former vice-president.

He has slipped from a dominant position in the large Democratic field to fourth place among voters in the crucial, first-in-the-nation Iowa caucus, according to a New York Times/Siena College poll released last Friday.

That survey put Senator Elizabeth Warren in the lead, at 22 per cent, followed by Senator Bernie Sanders, at 19 per cent, with a surging Mr Pete Buttigieg, mayor of South Bend, Indiana, at 18 per cent, one point ahead of the far better-known Mr Biden.

But many Democrats fear that Ms Warren and Mr Sanders are too liberal to win in a nationwide vote, and that Mr Buttigieg, who has struggled to widen his appeal beyond a core of white, liberal voters, might not be electable.

That also means less attention on the Democrats' top issues, including health care, gun control and immigration reform.

"I do think that, in the short run, impeachment will dominate Washington and political news reporting" and "will hurt candidates trying to crash into the top tier", said academic Chris Arterton, an emeritus professor of political science at The George Washington University.

The impeachment inquiry in the Democratic-led House centres on Mr Trump having linked military aid to Ukraine to a request that Kiev investigate the Bidens in a bid to obtain politically damaging information.

House committees have heard from a stream of witnesses expressing concern at the way Mr Trump dealt with Ukraine.

But in his combative appearance in Mississippi, Mr Trump insisted that the talk of impeachment was fuelling a Republican surge that would propel him to re-election next year.

"I tell you, the Republicans are really strong," he said, touting the emergence of "an angry majority".

Opinion surveys have shown increasing support among Democrats and some independents for impeachment, but a recent average of polls showed Mr Trump clinging to 42.8 per cent approval rating.

Mr Biden, a clear Democratic favourite when he announced his candidacy, has, meanwhile, been slipping - as reflected by his recent difficulties in fundraising.

For now, analysts continue to predict that even if Mr Trump loses an impeachment vote in the House, the Republican-dominated Senate would spare him.

Prof Arterton said he believes that House Democrats, led by speaker Nancy Pelosi, are determined to deal with the impeachment quickly so Democratic candidates can focus on the election.

"By February, when the presidential campaign really starts... I believe that the 2020 campaign will come to dominate the news," he said.

In the meantime, candidates such as Senator Amy Klobuchar and Mr Buttigieg "won't get the news coverage they might otherwise be able to garner".