WASHINGTON, Jan 5, 2024 (BSS/AFP) - Donald Trump will face US voters for the first time in years when Iowa's presidential nomination contest on January 15 offers the clearest insight yet into whether he can convert his expansive polling leads into a stunning White House return.

The Republican ex-president had looked out for the count after leaving Washington under a cloud following the 2021 assault on the US Capitol by a pro-Trump mob seeking to keep the defeated tycoon in power.

Out on bail in four jurisdictions and facing the potential collapse of his business empire in his native New York, his prospects have hardly improved during his years out of office.

Yet the 77-year-old showman has turned his legal woes -- 91 felony charges over business fraud, mishandled classified documents and a criminal conspiracy to overturn the 2020 election -- into a rallying cry to galvanize his loyal base.

He is now well-placed to be named the party's standard-bearer to take on President Joe Biden in November, with a commanding lead in polls and momentum in the early states that his rivals have been unable to blunt.

The RealClearPolitics polling average shows Trump leading the field in Iowa's caucuses -- where Republicans gather to pick their preferred nominee -- with 51 percent support.

Florida governor Ron DeSantis and former UN ambassador Nikki Haley trail at 18 percent and 16 percent, respectively.

Trump's campaign -- a more professional and focused operation than in previous elections -- hasn't been resting on its laurels, building a network of "precinct captains" to corral support in Iowa.

- Trump: disciplined, on-message -

Trump has been blitzing the state at rallies in front of large crowds where he has driven home with uncharacteristic discipline his message that immigration and border security are America's biggest issues.

"Joe Biden is leaving behind a catastrophe of historic proportions," he said in an op-ed Wednesday for the Des Moines Register, Iowa's largest newspaper.

"The next president must secure the border while also stopping inflation, saving the economy, cleaning up Washington corruption, restoring peace through strength, and preventing World War III."

DeSantis -- a hard-line populist and one-time Trump protege -- had been polling in second place nationally but has struggled after failing to usurp Trump early on and has slipped into third.

He is betting the farm on a strong showing in Iowa, where he has visited all 99 counties and won the endorsement of its popular governor.

Haley, in second place nationally but still more than 50 points behind Trump, is hoping her campaign will ignite at the January 23 primary in New Hampshire, a state with a better recent track record than Iowa for picking the eventual Republican nominee.

- Party united? -

Haley has campaigned on being more electable than Trump, who has sparked outrage -- and comparisons with Adolf Hitler -- for complaining of undocumented migrants "poisoning the blood" of America and promising mass deportations.

"We know Trump is going to win the caucus in Iowa," New Hampshire governor Chris Sununu said at an event Wednesday, arguing that a "strong second" from Haley would give her a chance in his state.

Recent polls show all three Republicans besting Biden in hypothetical general election match-ups.

Trump was stung by defeat in Iowa in 2016, the last time he was in a competitive primary, and aides have been clear they want to wrap up the nomination long before the Republican National Convention in July.

But they are also keen for the party to coalesce around the front-runner before multiple expected court dates in his legal battles.

As well as his criminal cases, Trump is being sued by a writer he has already been found to have sexually abused, and is facing $250 million in penalties and a ban on doing business in New York after being found liable for extensive bank fraud.

The Republican primary also features a number of low-polling candidates, from entrepreneur Vivek Ramaswamy to Trump antagonist Chris Christie, but none is expected to stay the course.

Biden theoretically has his own primary contest -- although his challengers, self-help author Marianne Williamson and Minnesota congressman Dean Phillips -- present no serious threat.

Iowa's Democrats will also attend caucuses -- meetings at which local members of a political party gather to register their candidate preferences -- on January 15 but will vote by mail from January until March.