By Gram Slattery

SIOUX CENTER, Iowa (Reuters) - Donald Trump used his first visit to Iowa this year to attack Republican competitor Nikki Haley and to hit back against Democratic President Joe Biden, who denounced him as a threat to American democracy earlier on Friday.

Speaking to a crowd of several hundred supporters just 10 days before the crucial Iowa caucus - the first round of the Republican nominating contest - the former president presented a dark portrait of the United States. He called it a "failing" nation, beset by "terrorists" and immigrants from "mental asylums" pouring over the U.S.-Mexico border.

He shot back at Biden, who spoke of the dangers of a potential second Trump term at an event in Pennsylvania earlier in the day. Biden, who will likely face Trump in a general election rematch in November, was particularly critical of Trump's conduct on Jan. 6, 2021, when a mob of his supporters attacked the U.S. Capitol as legislators were certifying Biden's 2020 election victory.

"Not one thing has gotten better under crooked Joe Biden. Everything's a mess," Trump said to several hundred cheering supporters at the rally in the state's rural northwest.

Trump only briefly addressed the events of Jan. 6, whose three-year anniversary is on Saturday, repeating unfounded claims that the 2020 contest was marred by widespread voter fraud.

Trump also directed his fire toward Haley, who served as U.S. ambassador to the UN for two years during his term. While Haley trails Trump by over 30 points in Iowa, she is much closer in New Hampshire, which holds the second contest of the Republican nomination process, and she has been rising in opinion polls in recent months.

"Nikki Haley has been in the pocket of the open borders establishment donors her entire career," Trump said. "She's a globalist."

COUNTDOWN TO CAUCUS

Several hundred supporters, some from neighboring states, waited for hours in freezing temperatures to enter the events hall in the town of Sioux Center where Trump spoke.

The size of the event, during which Trump talked for roughly two hours, dwarfed that of any recent campaign event held in the state by Haley or Florida Governor Ron DeSantis, another contender for the nomination.

Still, Trump's team is leaving nothing to chance. His aides are eager to avoid a repeat of the last competitive Iowa Republican caucus, in 2016, when Trump led in most polls, but ended up finishing second, due in part to a haphazard on-the-ground organizing effort.

His team had recruited 1,800 caucus captains as of mid-December, according to a senior campaign official, and had provided hundreds of training sessions. Under the caucus system, voters gather at pre-determined locations, and a representative for the major candidates gives a pitch on their preferred nominee. Later, those gathered cast their ballots. Iowa's Republican nominating contest is set for Jan. 15.

The Friday event started with a videocast tutorial, during which Lara Trump, the former president's daughter-in-law, explained the caucus process in detail. Dozens of people roamed the area in white hats, which indicated that they were caucus captains.

During the Friday event, Trump made light of a previous comment, in which he said that he would be a dictator on the first day of his presidency. He did not, however, explicitly walk that comment back.

Trump hits back at Biden, attacks Haley in first 2024 trip to Iowa