The number of Americans who think President Donald Trump should be impeached rose by eight percentage points in one week, according to a Reuters/Ipsos poll.

Last week, Democrats opened an impeachment inquiry to look into allegations that Trump leveraged military aid to Ukraine to pressure that country to investigate former Vice President Joe Biden, the president's chief political rival heading into the 2020 election.

A previous Reuters/Ipsos poll released on Sept. 24 found that 37% of all Americans thought Trump should be impeached and that 45% said he should not. A week later, the number saying he should be impeached rose to 45%, while the number saying he should not dropped to 41%.

Support for impeachment was clearly divided between registered Republicans and Democrats, with 13% of GOP voters saying the president should be impeached and 81% saying he should not. Among Democrats, 75% favored impeachment and 14% said they were opposed. And 38% of registered independent voters said Trump should be impeached while 39% said he should not.

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Sixty-four percent of Americans said they had heard "a great deal" or "some" about the Ukraine story while another 21% said they had heard about it but knew little of the details. Another 10% said they hadn't heard anything and 6% said they didn't know about the controversy.

The poll found Trump's job approval rating at 39%, down from 43% the previous week, and his disapproval rating at 56%, up from 54%. It also found him losing to the three leading contenders in the Democratic primary if the general election were held today. Biden bested Trump 39-34% in such a hypothetical matchup, Sen. Bernie Sanders of Vermont won 40-34% and Sen. Elizabeth Warren of Massachusetts topped him 38-34%.

The poll was conducted Sept. 26-30 and included 2,234 adults with a margin of error of plus or minus 2.4%.

Trump and his supporters have said the president was motivated by a concern about corruption in Ukraine and have alleged that Biden improperly used his influence as vice president to secure a job for his son Hunter Biden with a Ukrainian energy company.

When asked their take on the story, 43% of Americans told the Reuters/Ipsos pollsters that Trump is trying to smear Biden ahead of the election. Twenty-six percent said Biden is trying to cover up a scandal that could hurt him in 2020, and 31% said they weren't sure which version of events was true. Notably, 42% of independents thought Trump was trying to smear Biden while only 17% thought it was Biden trying to bury a scandal. Forty-one percent of independents said they weren't sure.

Americans did not seem to think it was unusual for an elected official to use the power of their office to smear a rival – with 74% saying they thought many officials already did so. But that did not mean they are OK with it: A majority (65%) agreed that officials who use their office to smear their rivals should be removed. And 66% of the respondents said officials who work with a foreign government to attack their rivals should be removed from office.

Registered Republicans were less certain, with 44% agreeing that a politician who uses their office to go after their opponents should be removed from office, while 41% disagreed. Similarly, 46% of Republicans agreed that an official who works with a foreign government to go after a rival should be removed, while 33% did not.

University of Michigan political scientist Nicholas Valentino told Reuters that he did not expect to see much more fluctuation in the numbers unless Republican leaders begin to break ranks and support Trump's impeachment.

"People aren’t constitutional scholars," Valentino told Reuters. "They trust their elected officials from their party to know the rules of politics. And when members of their own party say that someone has broken the rules, that’s when public opinion will really begin to change."

A poll released Monday by Quinnipiac University found that voters were split 47-47% on whether Trump should be impeached and removed from office. That represented a major swing from the week before when 37% said Trump should impeached and 57% said he should not. And 52% said they approved of the House of Representatives opening a formal impeachment inquiry, while 45% disapproved.

Poll:Americans approve of impeachment probe by slim margin, split on removal from office