As political battles raged across the talk shows and within both parties on Sunday, ahead of the Iowa caucuses which start the presidential primary season on 1 February, Jeb Bush fired a salvo from the margins of the Republican race.

Referring to Donald Trump, the GOP frontrunner who spent the weekend happily deepening his argument with his nearest challenger, Ted Cruz, Bush told NBC’s Meet the Press: “The guy’s entertaining, for sure. But … he’s not going not win the nomination. And I am.”

The former Florida governor’s confidence is not backed by polling data. According to the realclearpolitics.com poll average, on Sunday he sat in fifth place nationally.

That put the one-time favourite ahead of seven candidates in the still-crowded Republican field, but his 4.8% return left him nearly 30 points behind Trump (34.5%) and well adrift of Cruz (19.3%), Marco Rubio (11.8%) and even the retired neurosurgeon Ben Carson (9%), whose numbers appear to be in terminal decline.

Bush is off the pace in the two early voting states, Iowa and New Hampshire, polling at 4.5% in the first state and 8.4% in the second (an improved figure which nonetheless leaves him sixth, behind New Jersey governor Chris Christie and Ohio governor John Kasich). In recent history, only Bill Clinton, in 1992, has won a presidential nomination without taking either of those states.

Nonetheless, Bush continued to attempt to take the fight to Trump.

“He’s not a conservative,” Bush continued, explaining why he thought he was the only person to have gone after Trump on economic issues in Thursday night’s debate.

“Should the opportunity come up in the next debate to talk about [Trump’s] bankruptcies, I’ll do it. Four times bankrupt. He claims he was just using the law but a lot of people got wiped out because of that.”

Asked by host Chuck Todd what he thought was the secret of Trump’s success despite his own efforts against him – which now include an ad that quotes Bush calling Trump “a jerk” – the former governor said: “Well, there’s a lot anxiety. People are frustrated with Washington; they’re frustrated about their own lives.

A Jeb Bush political ad, entitled ‘Enough’.

“The big guy comes in and offers the moon and the stars, and people have latched on to that. But the reality is he’s not offering anything to lift people up.”

Bush declined to say, though, that he would not support Trump if the billionaire won the Republican nomination. The prospect of Hillary Clinton or Bernie Sanders being the next Democratic president was “chilling”, he said.

“I’m going to win this nomination, that’s my focus, that’s what I’m trying to do, but anyone would be better than Hillary Clinton or Bernie Sanders.”

Asked if it was time for the more moderate conservatives in the Republican field to unite and pick one candidate to stop Trump and Cruz, Bush avoided the question.

“New Hampshire and Iowa and South Carolina and Nevada are going to shape the contest in March,” he said, “and we have the resources and we’re on every ballot and I’m going to do it.”