Americans are split on whether they think the Justice Department's Russia investigation is fair and are unsure of special counsel Robert Mueller, but they overwhelmingly believe he should be allowed to finish his investigation, according to a new NPR/PBS NewsHour/Marist poll.

Fewer than half of Americans (48 percent) think the Russia probe has been fair, more than a quarter (28 percent) think it has not been and another quarter are unsure (23 percent).

Just 29 percent of Americans had a favorable impression of Mueller, while another 29 percent had an unfavorable one, and 42 percent said they're unsure or never heard of Mueller. Mueller is not only leading the Russia investigation but was the second-longest-serving FBI director since J. Edgar Hoover. (Mueller, a Republican, was FBI director under two presidents: George W. Bush and Barack Obama, from 2001 to 2013.)

Still, more than two-thirds (68 percent) say he should be allowed to finish the investigation. About 1 in 7, or 14 percent, say he should be fired.

And democratic institutions, particularly political ones, are not holding up well in this age of Trump.

"Mueller is not that well defined," said Lee Miringoff, director of the Marist College Institute for Public Opinion. And that makes him vulnerable to opponents who want to target him, Miringoff said. "An opponent could want to step in and define him; he's not going to define himself," Miringoff said, noting that Mueller is a prosecutor who has worked methodically with few leaks and kept details of the investigation private.

But, very publicly, conservatives have gone after the former FBI director on cable news and questioning his motivations. It has apparently worked. The views of Mueller are sharply divided by politics.

Democrats have a favorable impression of Mueller by a 49-to-14-percent margin. But Republicans are the polar opposite. They have just a 15 percent favorable to 40 percent unfavorable impression. And the conservative effort has apparently worked with independents as well. They are more split, but independents have a net-negative impression of him, 30 to 35 percent.

There is also a big split between whites with college degrees and those without. Those with a college degree view him favorably by almost 20 points (45 to 26 percent). Those without view him negatively, 24 to 31 percent.

"If this were a political campaign, you would be saying, 'Put up the ads,' " said Barbara Carvalho, director of the Marist poll, of Mueller's image.

There's also a partisan split on the fairness of the investigation. Democrats overwhelmingly view it as fair (72 to 10 percent). But just a quarter of Republicans view it as fair (26 percent) and half view it as unfair.

But for now, there is largely agreement that Mueller should not be fired – even 59 percent of Republicans say he should be allowed to finish the investigation.

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