According to public opinion polls, presidents seem to be most popular

As former President Donald Trump considers launching another bid for the White House, more than six in 10 Americans do not want him to run in 2024, according to a new PBS NewsHour/NPR/Marist poll. And while Trump's possession of more than 10,000 government documents at his Florida home seems not to have changed the minds of his steady supporters, a plurality of Americans think he has done something illegal.

The level of support for another Trump campaign remains virtually unchanged from December 2020, the month after he lost the presidential election and weeks before a mob of his supporters stormed the U.S. Capitol in an effort to stop the certification of the Electoral College votes.

"His numbers don't move. They're locked in," said Lee Miringoff, the director of the Marist Institute for Public Opinion. "The good thing for former President Trump is his numbers don't drop. The bad thing is he's only talking about a third of the electorate who are in his corner."

"That's not a great place to launch an election campaign," he added.

Just 28 percent of independents believe Trump should run again, this poll found, while two-thirds say the former president should sit out the next election. According to 2020 exit polling, 41 percent of independents had voted for Trump's reelection, suggesting a significant cratering of support since.

Jim Holladay, an independent voter from North Carolina, voted for Trump in 2020 but now says the former president should step aside.

"He's done some things that are borderline stupid. I don't think that kind of thing is going to help unite the country," Holladay said, citing the classified documents recently found in Trump's home and the former president's rally on Jan. 6.

WATCH: The political impact of what the FBI found at Mar-a-Lago

"I don't think he can win," he added. "I don't think he can pull the Republican Party together and win the election. I think too many people are scared of him."

Trump's potential candidacy has the consistent support of three groups. Two-thirds of Republicans, 70 percent of voters who supported his 2020 campaign and a little more than half of white evangelical Christians want Trump to run again.

"I don't think he can pull the Republican Party together and win the election. I think too many people are scared of him."

The opposition to a Trump candidacy is being driven largely by Democrats, with 90 percent hoping Trump does not run, according to this poll. But 9 percent of Democrats do want Trump to mount a comeback bid, including Adrian Thompson, who lives in the suburbs of Detroit.

Thompson, who voted for Joe Biden in 2020 but does not think the president should run for a second term, believes a Trump candidacy would invite an independent challenger like Republican Wyoming Rep. Liz Cheney to join the race, splitting Republican-leaning voters and giving a boost to the Democratic nominee. While no candidates have announced a bid for the GOP presidential nomination, former Vice President Mike Pence and Florida Gov. Ron DeSantis are also frequently mentioned as would-be competitors that could shake up the primary campaign.

"It's not that on a personal level I want [Trump] to run. It's not on a personal level that I agree with him in any way," Thompson said. "With him running, what otherwise I think would be a surefire win for any Republican candidate with the general state of the global economy, I just think it would help a Democrat."

The poll was conducted in the lead up to Biden's speech in Philadelphia, where he stepped up his criticisms of his predecessor and warned that Trump and his supporters "represent an extremism that threatens the very foundations of our Republic."

Would Trump's support change if he were charged with a crime?

The former president faces a handful of investigations, including from the Department of Justice and the U.S. House select committee on the origins of the Jan. 6 attack, a grand jury looking into potential election interference in Georgia and, most recently, an FBI probe into classified materials removed from the White House and kept at Trump's Florida estate. Some had been recovered or returned earlier this year. But when the FBI executed a search warrant at Mar-a-Lago last month, agents still found more than 100 classified documents and 43 empty folders with classified markings, among thousands of other official records, according to a Department of Justice list of items.

Support for Trump's candidacy in 2024 would not change much if any of these investigations result in Trump being charged with a crime, according to this poll. Sixty-five percent of Americans would oppose another run for the White House. More than six in 10 Republicans would still want to see him launch a campaign. Meanwhile, 73 percent of independents say he should not run again if he is charged.

WATCH: Legal implications of decision to appoint special master to review Trump documents

This poll is just a snapshot of the current political environment. With two months until the midterm elections and another two years until the 2024 presidential election, a lot can still change – with the Republican primary field and the investigations.

When it comes to the cache of documents found at Mar-a-Lago, there are still some critical pieces of missing information before the Justice Department can make a case for criminal prosecution, including evidence or testimony that directly puts the records in Trump's hands, according to national security attorney Mark Zaid. "That would be the smoking gun," he said.

"The pendulum is swinging much more towards linking him to direct contact with some of these documents," he added. "You had three documents found within or on his office desk. So it makes it more likely that he would have known about them or even took them himself."

A redacted FBI photograph of documents and classified cover sheets recovered from a container stored in former President Donald Trump's Florida estate, and which was included in a U.S. Department of Justice filing and released on Aug. 30, 2022. Photo via U.S. Department of Justice/Handout via REUTERS

Trump lost access to classified documents when he left the White House in January 2021. Weeks later, Biden said he would not extend to Trump the courtesy of regular intelligence briefings that former presidents traditionally receive. Biden cited Trump's "erratic behavior" in the lead up to the Jan. 6 attack and the risk Trump "might slip and say something" about the information he learned.

"If [the documents] are classified, then he does not have authority to possess them at all," Zaid said, because aside from lack of clearance, Trump does not have a secure facility at Mar-a-Lago to store them.

"If [the documents] are classified, then he does not have authority to possess them at all."

Even non-classified documents from Trump's term in office are the property of the federal government, he added, since former presidents are required by the Presidential Records Act to turn over records to the National Archives when they leave office.

"I do not think we would see a prosecution for possession of [nonclassified records]. There are criminal statutes that could apply if you jaywalk, and what are the odds you're going to get ticketed for jaywalking?" Zaid said. "If [Trump] or anyone around him gets prosecuted, it's going to be for the classified information and the obstruction. If there had been no obstruction, there probably would never be prosecution."

Altogether, nearly half of Americans believe Trump should be charged with a crime. Forty-four percent believe Trump has done something illegal, including 42 percent of people who believe he's done something illegal and should be charged with a crime. Seventeen percent say he has done something unethical but not illegal. About a third of those people still believe he should be charged with a crime.

Twenty-nine percent say he has done nothing wrong, while 10 percent either have not heard about the FBI search or are not sure what to make of Trump's actions.

Unsurprisingly, views of Trump's actions break down largely along partisan lines in the latest poll. More than eight in ten Democrats say Trump has done something illegal, a view shared by 44 percent of independents and just 5 percent of Republicans. Meanwhile more than 60 percent of Republicans say he's done nothing wrong, an opinion shared by 28 percent of independents and just 1 percent of Democrats.

READ MORE: New poll asks Americans whether Trump should face charges, top midterm priorities

The poll was conducted before a Florida judge on Monday authorized Trump's request for an appointment of an independent special master to review the seized documents, blocking the Department of Justice from using the documents until that review is complete. While the DOJ investigation is likely to move forward, it may be months or even longer before any potential charges are filed, according to Chuck Rosenberg, a former federal prosecutor and FBI official.

"There is a longstanding Department of Justice policy not to bring charges or to take overt investigative steps near the time of an election," Rosenberg told PBS NewsHour anchor and managing editor Judy Woodruff last week. "They may go quiet for a time, but that doesn't mean the investigation has stopped. You can still do things covertly, quietly, secretly to further your investigation while you're in this pre-election quiet period."

PBS NewsHour, NPR and Marist Poll conducted a survey Aug. 29-Sept. 1 that polled 1,236 U.S. adults (margin of error of 4.1 percentage points) and 1,151 registered voters (margin of error of 4.3 percentage points).