Macon (US), Nov 5 (AFP) Donald Trump and his Democratic rivals have made frenzied, final pushes to motivate their core voters ahead of contentious midterm elections seen as a referendum on the president's divisive first two years in office.

Both sides say voter turnout will be key. Trump was on a hectic schedule of campaign appearances for Republican candidates 48 hours before Americans deliver their verdict at the ballot box, while former president Barack Obama made a last-ditch appeal for an endangered Senate Democrat in Indiana.

"You gotta get to the polls on Tuesday, and you gotta vote," Trump implored a crowd in Macon, Georgia, where he campaigned Sunday for the Republican candidate for governor in one of the country's tightest major races.

"The contrast in this election could not be more clear." Political passions have risen to a rare peak, with early voting in some states already running far ahead of normal levels.

"It's all about turnout," Senator Chris Van Hollen told "Fox News Sunday", as Democrats wage what polls say is an uphill battle to win control of the US Senate. Democrats are far better positioned for reclaiming a majority in the House, experts and polls say.

But in the first midterm under Trump -- an utterly unconventional president -- there are many unknowns, above all the bottom-line impact of a president who has driven both supporters and foes to a rare fever pitch of emotion.

"I can't speak to the blue, but I can speak to the red," Trump said earlier of Democrats and Republicans. "There is a lot of energy out there."

The party of a first-term president tends to lose congressional seats in his first midterm. But a healthy economy favours the incumbent -- and the US economy has been growing with rare vigour.

A new Washington Post-ABC News poll released Sunday suggested that while Democrats retain an edge in their battle for the House, Republicans could profit from increasingly positive assessments of the economy and by Trump's harsh focus on border security.

It found registered voters preferred Democratic candidates for the House over Republicans by 50 per cent to 43 per cent; but that was down from a 14-point advantage in August.

A second poll, by NBC and The Wall Street Journal, also showed Democrats holding the same seven-point advantage over Republicans.

But in what could be a sharp warning sign for Republicans, that poll reported college-educated white women -- the so-called suburban moms seen as crucial to the 2018 outcome -- favour Democrats by a substantial 61 per cent to 33 per cent.

Another wild card: The campaign's closing days come just a week after a gunman, who allegedly hated immigrants and Jews, killed 11 people at a Pittsburgh synagogue. A fanatical Trump supporter was also arrested on charges of mailing pipe bombs to prominent opponents of the president, including Obama.

The president's critics say the highly-charged atmosphere he has helped create made the two attackers feel sufficiently comfortable to carry out their crimes.

Republicans, trying to move past that, have been enthusiastically pressing the economic argument. But the president -- to the unease of some in the party -- has instead used his nearly nonstop schedule of campaign rallies to keep the spotlight on what he calls the security threat from migrants seeking to enter the nation through Mexico.

"We're not letting these people invade our country," Trump declared.

Democrats, meantime, painted sharp distinctions with Trump, insisting that only they will protect the health care gains made under Obama, that Trump has employed inhumane measures to keep migrants out, and that the divisiveness he has fostered must end.

And while Obama said Democrats would support a "kinder version of America", he did what many Democratic candidates have refrained from doing: directly challenging the president.

"There's got to be consequences when people don't tell the truth, when words stop meaning anything. When people can just lie with abandon, democracy can't work," he told a cheering crowd as he campaigned for Senator Joe Donnelly. "The only check right now on the behaviour of these Republicans is you and your vote."

Democrats face their toughest political map in decades in the Senate, which Republicans currently control 51-49. It is more favourable in the House, where Democrats need to gain 23 seats to take control of the 435-seat chamber. Election analysts at website FiveThirtyEight.com put the likelihood of Democrats winning the House at 85 per cent.

One key barometer of a midterm's direction is the presidential approval rating, and in Trump's case it is underwater, worsening in the last week to 54 per cent disapproval versus 40 per cent approval, according to public opinion pollster Gallup.

The two parties are also battling over dozens of governor's races, including tight high-profile contests in Georgia and Florida, where two Democrats are seeking to make history as the first African-Americans to lead those states. (AFP)

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