As US President Donald Trump’s impeachment trial is being paused for some time, four senators rushed to Iowa on Friday and joined top rivals for a final weekend of campaigning ahead of the presidential election.

After a Senate vote paved the way for Trump’s acquittal of charges of abuse of power and obstruction of justice, the impeachment trial was put on hold, allowing all candidates to enjoy a breathless final 72 hours of campaigning before the Iowa caucuses.

According to the recent polls, a tight contest in the heartland state, where former vice president Joe Biden this week has been taking his “Soul of the Nation” bus tour to all corners in hopes it will help him cross the finish line in the top spot on Monday.

Biden, 77, “is making the case that this is no time to take a risk on someone new,” Buttigieg, who at 38 is less than half Biden’s age, told a crowd at the Masonic Temple in the town of Clinton, Iowa.

The contest to see who challenges Trump in November’s election is a months-long slog, and those with minimal support have been peeling off. Former congressman John Delaney dropped out Friday.

On December 18, President Trump was formally impeached in a historic vote in the House of Representatives.

Democrats, who control the House of Representatives and led the investigation, accuse Trump of manipulating Ukraine by withholding nearly $400 million in military aid for its war against Russian-backed separatists and a White House meeting for Zelensky until the latter announced a Biden probe.

Earlier, Democratic presidential candidate Joe Biden confronted a voter by calling him a liar, suggesting that the former Vice President had sent his son to work in Ukraine.

According to SurveyUSA poll, Biden enjoyed the support of 32 per cent of likely Democratic primary voters nationwide, while Massachusetts Senator Elizabeth Warren garnered 22 per cent backing as runner-up.

Nearly half of Democratic Iowa voters said they remained undecided before Monday’s caucuses, the local meetings where participants align behind their candidates in one of the country’s quirkier voting systems.

Biden’s blue-collar roots and his uncanny ability to connect personally with voters are huge assets in a state used to face-to-face encounters with candidates, although his Iowa speeches have lacked the passion that animates some rivals.

Despite the agonizing over which political approach to take — revolution or realism — in the 2020 election, Iowa’s Democratic Party chairman Troy Price said voters have unified around one goal.

(With inputs from agency)