Even relative outsiders Pete Buttigieg and Cory Booker are both five percentage points ahead of Trump.
Polling in the US election should of course be approached with caution – Trump defied almost all the major predictions when he won in 2016.
But that didn’t stop the president himself from taking umbrage at the poll, which was widely reported in the media.
In two tweets, he said: “The Fake News has never been more dishonest than it is today. Their new weapon of choice is Fake Polling, sometimes referred to as Suppression Polls (they suppress the numbers). Had it in 2016, but this is worse.....”
“The Fake (Corrupt) News Media said they had a leak into polling done by my campaign which, by the way and despite the phony and never ending Witch Hunt, are the best numbers WE have ever had. They reported Fake numbers that they made up & don’t even exist. WE WILL WIN AGAIN!”
The outburst came as Trump and former vice president Joe Biden repeatedly laid into each other in the battleground state of Iowa, unleashing verbal attacks that at times felt more appropriate for the final weeks before election day than a lazy summer about 17 months before voters go to the polls.
The exchange laid bare the rising political stakes for each man.
Trump zeroed in on Biden as a threat to his re-election chances and is testing themes to keep him at bay, the Press Association reports.
Biden, meanwhile, is campaigning as a front-runner with near-universal name recognition, relishing the fight with Trump while trying to ensure he does not ignore the demands of the crowded Democratic primary.
“People don’t respect him,” Trump said of Mr Biden after touring a renewable energy facility in Council Bluffs.
“Even the people that he’s running against, they’re saying: ‘Where is he? What happened?’”
With a dose of exaggeration, the president added: “He makes his stance in Iowa once every two weeks and then he mentions my name 74 times in one speech. I don’t know.
“That reminds me of Crooked Hillary. She did the same thing.”