The poll found just 34% of Americans feel the president has told the truth when it comes to Mueller's probe.
Comparatively, back in August 38% of registered voters said they agreed Trump had been honest and truthful about the investigation, while 56% said they did not agree he'd been truthful.
This comes amid mounting legal pressure for Trump in relation to Mueller's probe, and discussions on whether or not he can be indicted as a sitting president.
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Trump was recently implicated in serious crimes by federal prosecutors in relation to hush money payments made by his former personal attorney Michael Cohen to two women who said they had had affairs with Trump. Prosecutors said the payments represented campaign finance violations, and are among the reasons Cohen was sentenced to three years in prison last week.
Cohen in August pleaded guilty to eight federal crimes in the the Southern District of New York, including campaign finance violations linked to the payments. At the time, Cohen said he made the payments at Trump's direction and did so to influence the 2016 election.
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In a recent interview with Fox News, the president denied directing Cohen to make the payments to hide the alleged affairs from the public.
"I never directed him to do anything wrong," Trump said. "Whatever he did he did on his own. He's a lawyer. A lawyer who represents a client is supposed to do the right thing, that's why you pay them a lot of money."
As part of the investigation he's leading, Mueller is looking into whether Trump colluded with Russia. The president has vehemently denied colluding with the Kremlin in any way, and routinely refers to Mueller's probe as a "witch hunt."