He lashed out at Evan McMullin, the independent presidential candidate who surpassed Johnson in Utah and is almost tied with Trump and Clinton there

The Libertarian candidate for president, Gary Johnson, has said the chance of Congress backing his economic policy is “probably pretty nil” and accused an independent rival of playing the role of “spoiler” in Utah.

Johnson lashed out at Evan McMullin, the conservative presidential candidate who has leapfrogged him in the state and now has a chance of becoming the first third-party or independent candidate for White House to win a state since 1968.

One recent poll showed McMullin almost tied with Donald Trump and Hillary Clinton in Utah. In contrast, Johnson, who set up his presidential campaign headquarters in Utah, is a very distant fourth.

“It’s a bit of a stretch to be comparing my candidacy with his,” Johnson said during a tense interview with the Guardian’s Anywhere But Washington series.

“He’s ensuring that Hillary Clinton will win Utah. You know what? He is what he is, and I begrudge no one for entering the race,” he said.

The Libertarian candidate added of his rival: “I think that he is splitting the Republican vote. And Utah being predominantly Republican, I think he’s splitting the vote, that Hillary will actually win the state.”

Johnson dismissed the suggestion that he was using the same “spoiler” argument that has been used against third-party candidacies such as his own. “I’m not labeling it spoiler, I’m just telling you what I think the reality is,” he said.

Johnson’s national poll numbers have plummeted since August, despite running in an election year in which the Republican and Democratic nominees have exceptionally low favorability ratings.

The Libertarian was hovering around 10% in national surveys, but after a series of embarrassing interviews – including one in which he appeared not to have heard of the Syrian city of Aleppo, and another in which he could not name a foreign leader he respects – he is now languishing around 6%.

In his interview with the Guardian, Johnson complained that interviewers were now treating him like “a dummy” and bristled when he was pressed on his decline in the polls.

“Why are you even interviewing me? I don’t get it. If I’m doing so poorly, is this to preside over a funeral here? It’s not a funeral! It’s a celebration!”

In another awkward exchange, Johnson defended his unorthodox economic policy, an extreme neoliberal proposal that includes the abolitions of income tax, corporation tax and the Internal Revenue Service.

When pressed on the details of his signature plan, which would replace existing tax infrastructure with a single consumption tax, Johnson said it had virtually no chance of being enacted in the US.

“Congress would have to pass that in the first place,” he said. “The chances of them passing that are probably pretty nil.”

Johnson insisted, however, that he stood by his tax plan. “I’m not doing this in a vacuum. The entire Chapman University economics department have helped me throughout this. Jeff Miron, my economics adviser [has helped]. They do point out that it it would be obviously a dramatic shift, but it would be simplification.”