A majority of self-described American voters surveyed in a new INSIDER poll agreed with Republican Rep. Justin Amash that President Donald Trump "committed impeachable offenses."

Among respondents who said they were registered to vote, 54% agreed.

Amash is the first Republican lawmaker to call for Trump's impeachment based on Robert Mueller's findings in the special counsel's Russia investigation.

In the wake of Mueller's report, and of a news conference the former FBI director gave last week, calls for Trump's impeachment have grown steadily louder.

House Democrats have been pumping the brakes on impeachment out of fear of political backlash. But mounting public support for the move could lead to a shift in Democrats' strategy.

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A majority of US self-described voters in a new INSIDER poll agreed with Rep. Justin Amash of Michigan that President Donald Trump "committed impeachable offenses."

Amash made headlines last month when he became the first Republican lawmaker to call for Trump's impeachment, based on what was contained in the report on the special counsel's Russia investigation. He also accused Attorney General William Barr of deliberately misrepresenting the special counsel Robert Mueller's findings and of trying to "sell the president's false narrative" about the report to the public.

But Amash said that despite Barr's portrayal of the Mueller report, Trump's actions "meet the threshold for impeachment" and that Trump most likely would have been indicted on obstruction-of-justice charges had he not been president.

Read more: Democrats are divided as ever on impeachment after Mueller punted the question to Congress

According to INSIDER's poll conducted May 31 to June 2, 51% of respondents agreed with Amash's statement, and, within that, 31% said they "strongly agree."

Among respondents who said they were registered to vote, 54% agreed. Twenty-four percent of such respondents disagreed with Amash's statement, with 17% saying they "strongly disagree." Seventeen percent said they neither agreed nor disagreed, and 8% said they didn't know.

Among respondents who said they were likely to vote in the 2020 Republican primary, about 17% agreed or strongly agreed with Amash's statement.

Calls for impeachment grow louder after Mueller's public statement

House lawmakers have been grappling with how to proceed on the impeachment question since Mueller's report was released in April.

While many progressive Democrats and 2020 presidential candidates support launching impeachment proceedings, mainstream lawmakers like House Speaker Nancy Pelosi and the House Judiciary Committee's chairman, Jerry Nadler, say they won't move forward on impeachment unless there is broad public support for it.

Several polls conducted in early May found that a majority of Americans opposed impeachment hearings.

Read more: Mueller says he won't make any more public statements on the Russia investigation, but his own words bolster the case for Democrats to have him testify before Congress

But the calls to impeach have been growing louder in recent days, particularly since Mueller gave his first public statement on his findings last week.

Many mistakenly believe the Mueller report 'exonerated' Trump of 'any wrongdoing'

It's unclear what prompted the shift because Mueller didn't reveal anything new in his remarks (much of what he said was included in his report). But some legal experts have suggested that Mueller saying many of his key conclusions out loud, even if directly quoted from the report, may have swayed public opinion in favor of impeachment.

Indeed, only 3% of respondents in a recent CNN poll said they had actually read Mueller's entire report. And as one GOP voter told NBC News, Amash's remarks were the first time she heard that Mueller did not exonerate the president.

"I was surprised to hear there was anything negative in the Mueller report at all about President Trump," Cathy Garnaat told the outlet. "I hadn't heard that before I've mainly listened to conservative news and I hadn't heard anything negative about that report and President Trump has been exonerated."

A Quinnipiac poll from early May found that 76% of Republicans and 11% of Democrats wrongly believed Mueller cleared Trump of "any wrongdoing." Overall, 38% of Americans thought Mueller had competely exonerated Trump, the poll found.

Meanwhile, an INSIDER poll conducted in April asked voters whether pursuing Trump's impeachment was a good use of House Democrats' time.

Twenty-two percent of respondents who identified as neither liberal nor conservative said impeachment was an "extremely" or "very good" use of their time. Thirty-two percent of slightly liberal voters said the same, as did 34% of moderately liberal voters and 50% of very liberal voters.

But in the days since Mueller's news conference, most of those numbers saw an uptick, indicating that a rising portion of Democratic voters believe Trump should be impeached.