Hillary Clinton and Donald Trump. (Getty Images, Reuters)

How can you tell if a politician is lying? His lips are moving.

This election cycle, the age-old adage is ringing true for a broad swath of voters. In a recent CBS News poll, 67 percent of respondents found Hillary Clinton to be dishonest, and 56 percent thought the same of Donald Trump.


Although those numbers may be similarly high, few would contend that Clinton's and Trump’s deceptions — broadly construed to include exaggerations and omissions — are the same.

Clinton’s deceptions tend to be defensive — her reputation is under attack and she’s trying to save face. As determined by PolitiFact, a political fact-checking service, her false statements often come in response to scandals and allegations against her. For instance, with regard to her private email server, she has said she “never received nor sent any material that was marked as classified” and that the server “was allowed” at the time. Both proved false.

Trump’s deceptions, by contrast, are more on the offensive, more self-promotional. He exaggerates his successes in the business world. He called his book "The Art of the Deal" the “best-selling business book of all time.” It’s not, according to PolitiFact.

And he creates allegations against his political opponents and minority groups out of thin air, making himself appear better by comparison. Among his false statements, according to PolitiFact: Hillary Clinton “invented ISIS,” even though the group predates Clinton’s tenure as secretary of state. The United States is allowing “tens of thousands” of “vicious, violent” Muslim terrorists into the country every year. This attempt to justify his ban on Muslim immigration was also found false.

That distinction between Clinton and Trump — offensive vs. defensive — has major implications for whether people view their lies as “legitimate” and morally acceptable, according to Matthew Gingo, a psychology professor at Wheaton College.

“Me lying to get myself out of trouble is not nearly as bad as me lying to get someone else in trouble,” Gingo said. “People view defense as more legitimate, such as physical self-defense.”

This has long been the consensus of psychological research. A 2007 study presented scenarios where people lied with varying motivations and interviewed people about how “acceptable” each lie was. They found self-protective lies (think Clinton) to be more acceptable than self-promotional lies (think Trump on his business record), which are more acceptable than self-promotional lies that harm others (think Donald Trump on Mexicans). A similar 1997 study of women found the same result, as did a 1986 study.

So Clinton’s omissions of fact, research tells us, should be perceived better than Trump’s flagrant scapegoating. Especially considering this disparity: PolitiFact has evaluated 203 of Trump's statements and 226 of Clinton's. It rated just fewer than a third of Clinton's as "mostly false" or worse but rated 71 percent of Trump's the same way.

But there’s another layer of complication here.

With Clinton, “there’s a lot more interleaving of truth and lies,” says Kim Serota, a marketing professor at Oakland University who has studied deception and political communication.

No one will ever know what exactly Clinton’s intentions were with her private email server, but anyone could find that the majority of Mexican immigrants are not, in fact, criminals and rapists. This makes Clinton’s deceptions appear more like “cover-ups,” Gingo says, which harms her public perception.

This is no surprise to a well-read psychologist. A 2006 literature review covering 206 studies on lie detection found that people who are motivated to be believed tend to appear more deceptive to others. Cover-ups, which tend to be planned and calculated, have more of this motivation behind them than Trump’s off-the-cuff statements.

So even though research tells us that people should be much more put off by Trump’s deceptions than Clinton’s, her apparent motivation to be believed lessens that disparity.

Regardless of what the public perception is, experts see Trump as taking common political deception to another level. “I’ve studied many people who don’t want to tell the whole truth,” Bella DePaulo, a project scientist specializing in psychology at the University of California at Santa Barbara, wrote in an email. “But they don’t want to tell outright lies, either. So they will do things they can defend as truthful.” Such as telling your friend who acted in an insufferable play that you thought his costume was well constructed.

But Trump is another story — or rather, tells other stories. “He is unapologetic about saying things that are completely and verifiably untrue,” DePaulo said. Experts find Clinton’s lying habits to be more “normal” among politicians in this respect.

“I think Trump is borderline pathological,” Serota said. “But the only person that would know that for sure is his psychologist.”