Trump parachutes into Iowa to rage against 'radical' Democrats
Trump in Iowa (AFP)

US President Donald Trump parachuted into Iowa on Thursday to scorch "radical" Democrats days before the state kicks off their party's nomination process, telling voters the opposition will suffer another crushing defeat in November's election.

At a rally in Des Moines, the capital of the agricultural state that plays a vital role in the Democratic primary, Trump denounced the "madness" of the far left and said only he could keep the US economy humming.

"This November, we're going to defeat the radical socialist Democrats that are right down the street," he boomed, as a rowdy crowd responded with multiple chants of "USA! USA!"

The notoriously vindictive leader took aim at several of the Democratic candidates: "Crazy" Senator Bernie Sanders; "Sleepy Joe" Biden, the former vice president; and former Indiana mayor Pete "Boot Edge Edge" Buttigieg.

Candidates are locked in a tight race days before the caucuses in Iowa, where countless volunteers are knocking on doors seeking to sway undecided voters, and political advertising is carpet-bombing the airwaves.

Divergent political views suggest Democrats remain undecided on which path to take in the general election, and Trump mercilessly mocked the radical left-leaning approach from candidates like Sanders, who advocates for universal health care and tuition-free college.

In a strong hint of how Trump will go after his Democratic rivals in the general election, the president growled over how "leftwing extremists" want to raise taxes, cancel health care plans, "destroy" Social Security, confiscate guns and open borders.

"The Democrats will lose because America will never be a socialist country," he said.

Trump's high-energy speech lasted 90 minutes, and he made clear he believed attendees were getting a star performance. "I work my ass off up here, OK?"

While Democrats have clashed against each other on policy, performance or personalities, Biden has pivoted directly towards the president, making the case for a Biden-Trump showdown.

"I can hardly wait to debate this man," Biden told a crowd in Waukee, a whistlestop on his weeklong bus tour across the state, hours before Trump landed.

Trump is trying to obliterate the healthcare law known as Obamacare, ignores the threat of climate change and has "walked away from our allies and embraced dictators and thugs," the 77-year-old Democratic party elder added.

After a yearlong campaign warmup, Iowa's winner will pocket critically important momentum as the contest shifts to New Hampshire and then Nevada and South Carolina, the early-voting states in the nomination process.

With a dozen candidates making their final Iowa pitches, the race is tight. Sanders, a 78-year-old running as a Democratic socialist, is leading the charge in the state, with Biden hot on his heels.

Two more candidates, centrist Buttigieg, 38, and progressive Senator Elizabeth Warren, 70, are within striking distance, with a fifth candidate, 59-year-old Senator Amy Klobuchar, in the second-tier but hoping to land a major upset.

Trump hammered Democrats over their efforts to remove him from office via the ongoing Senate impeachment trial that has infuriated the Republican base.

"We're having probably the best years that we've ever had in the history of our country -- and I just got impeached! Can you believe these people?" he huffed.

"No, that's not gonna work. Watch."

Trump was impeached in December by the Democratic-led House of Representatives for abuse of power and obstruction of Congress, but he is expected to be acquitted by the Senate's Republican majority.

Despite the stain of impeachment, and the awkward imagery of Trump rallying while some networks carried live coverage of the trial, his supporters sang his praises.

"I love him. I am so sick and tired of what the other party is doing to him and trying to take him down," retiree Linda Moon, 72, told AFP outside the rally.

"He isn't perfect," she added. "But he's doing really good things in this country."

With many Iowa Democrats still undecided, the race remains fluid.

But the party's statewide chairman, Troy Price, said the large number of uncommitted voters close to the caucus was due to "so many great candidates" running.

Iowans are "so ready for a change," Price said. "They're tired of the fighting, they're tired of the broken promises that this president has made."

Complicating matters, Sanders, Warren and Klobuchar have been tied to Washington for Trump's trial, denying them crucial face time with fastidious Iowa voters.

While Biden and Buttigieg hop-scotch around Iowa, the senator hopefuls are reduced to surrogates campaigning in their stead.