Trump’s rivals in Iowa still think they can win but could the millions of dollars his rivals are still spending overhaul him.

On a bitterly cold morning last week, Marlys Popma stepped into Newton Community College as an undecided voter.

After emerging an hour later, she was determined to vote for Nikki Haley.

Republican activist’s mind was changed by the former UN ambassador’s short speech that demonstrated her competence and empathy to a small conference room crowd.

“Be bold,” Ms Popma encouraged her fellow Republicans in the room after telling them she backed Haley, to applause.

In addition, she made a thinly veiled reference to Donald Trump’s commanding lead in the polls.

Ms Popma advised, “Don’t be afraid to support the person you want to support just because you think someone else will win.”

Candidates vying for Republican nomination will face their first real-world test in the Iowa caucuses on 15 January.

During a caucus, people attend a meeting before they vote on their preferred candidate, perhaps by head count or show of hands.

It is likely that the winner of the state-by-state contests will face Trump’s rivals Democratic Vice President Joe Biden in the November 2024 presidential election.

An Iowa State University poll published last week found that 54% of likely caucus-goers favored Mr Trump over Florida Governor Ron DeSantis, Ms Haley and Vivek Ramaswamy, a biotech millionaire.

In contrast with Ms Haley’s $3.5 million pledge and Ramaswamy’s eye-watering $8 million promise, Mr DeSantis has set aside $3.3 million (£2.6 million) to spend on Iowa advertising in November and December.

At a forum in Des Moines held by influential Christian organisation The Family Leader, pastor and social worker Philip Herman says voters are open to hearing more, even as election day in Iowa nears.