Only 40% of Republicans believe President Donald Trump asked Ukraine to investigate Joe Biden, according to a new Monmouth University poll, even though a memo released by the White House shows that he did.

The Monmouth poll found about 62% of Americans "believe it is likely that Trump mentioned the possibility of an investigation into Biden" during his July 25 phone call with Ukrainian President Volodymyr Zelensky.

The July 25 phone call between Trump and Zelensky is at the heart of a whistleblower complaint that accuses Trump of using the power of his office to solicit foreign interference in the 2020 election.

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President Donald Trump has publicly admitted he discussed Joe Biden with Ukraine and the White House released a memo on his July 25 phone call that shows he asked his Ukrainian counterpart to investigate the former vice president and his son, Hunter Biden. Still, only 40% of Republican voters believe he did so, according to a Monmouth University poll released Tuesday.

The Monmouth poll found about 62% of Americans "believe it is likely that Trump mentioned the possibility of an investigation into Biden" during his phone call with Ukrainian President Volodymyr Zelensky. Meanwhile, 15% say he probably did not do this and 23% are unsure.

Split across partisan lines: 85% of Democrats believe Trump mentioned investigating Biden in the call compared to just four-in-ten Republicans.

And even among Republicans who have heard a lot about the call, just 50% believe Trump asked Ukraine to open such an investigation, according to the poll.

Among all Americans who have heard a lot about the call: 76% say "this conversation probably occurred," 12% say it probably did not, and 12% are unsure.

Read more: Trump's actions with Ukraine were 'profoundly stupid' and beyond anything any president has ever done, historians and veteran diplomats say

A little over half of the public (52%) has heard "a lot about reports that Trump asked the Ukrainian president to investigate Joe Biden and his son," the poll found, while 27% have heard a little about this, and 21% have not heard anything. More Democrats (62%) than Republicans (52%) said they've heard a lot about this.

Meanwhile, the poll found 63% of Americans said it's not appropriate for a president to make this type of request of a foreign leader.

"At the very least, it is clear from the readout that Trump discussed investigating Biden during the call. Even though this information was released by the White House itself, more than one quarter of Republicans still say Trump probably didn't make any mention of it. This seems to be another example of partisan tribalism at work in public opinion," Patrick Murray, director of the independent Monmouth University Polling Institute, said in a statement on the poll.

Here's what we know about the Trump-Zelensky call:

The July 25 phone call between Trump and Zelensky is at the heart of a whistleblower complaint that accuses Trump of using the power of his office to solicit foreign interference in the 2020 election.

Prior to the public release of the White House memo on the call, which was closely followed by the release of the complaint, Trump acknowledged discussing Biden with Zelensky.

"The conversation I had was largely congratulatory, with largely corruption, all of the corruption taking place and largely the fact that we don't want our people like Vice President Biden and his son creating to the corruption already in the Ukraine," Trump told reporters on September 22.

The White House memo on the call shows Trump stating to Zelensky: "There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that so whatever you can do with the Attorney General would be great. Biden went around bragging that he stopped the prosecution so if you can look into it … It sounds horrible to me."

Trump has also tweeted about the conversation and mentioned the Bidens. On September 30, he said, "Very simple! I was looking for Corruption and also why Germany, France and others in the European Union don't do more for Ukraine. Why is it always the USA that does so much and puts up so much money for Ukraine and other countries? By the way, the Bidens were corrupt!"

And the whistleblower, citing White House officials with direct knowledge of the call, said Trump "pressured" Zelensky to "initiate or continue an investigation into the activities of former Vice President Joseph Biden and his son, Hunter Biden."

The acting Director of National Intelligence Joseph Maguire said the complaint was "in alignment" with the White House memo on the call.

Trump urged Ukraine to investigate Biden over baseless allegations regarding the former vice president's role in seeing a prosecutor ousted and Hunter serving on the board of a Ukrainian gas company, Burisma Holdings. There's no evidence of wrongdoing on the part of either Biden.

Trump's primary allegation is that Biden pressured Ukraine to fire a prosecutor on behalf of his son, but from what is currently known this is not true, and the former vice president was among a number of US and European officials to push for the ouster of the prosecutor.

The prosecutor, Viktor Shokin, was accused of slow-walking Ukraine's efforts to root out corruption. And though he'd previously overseen investigations into Burisma, by the time he was pushed out the probe was dormant.

Read more: Trump says Democrats are wasting the country's time on 'BULLSHIT' in angry tweet on impeachment

Regardless of the available information, Trump has seemingly convinced a significant portion of voters that Biden pushed for Shokin to be fired for his son's benefit. Monmouth found 42% of Americans say Biden "probably did exert this pressure" and 37% say this probably did not happen.

The Ukraine scandal has sparked an impeachment inquiry into Trump. According to the Monmouth poll, 44% of Americans feel that Trump should be impeached and "compelled to leave the presidency," while 52% do not want to see him impeached. That marks an increase since Monmouth polled on this question in August and 35% supported impeachment while 59% did not.