WASHINGTON (AP) — Donald Trump is fickle about the Fifth.

In 1990, he invoked his Fifth Amendment right to avoid self-incrimination by refusing to answer 97 questions in a divorce deposition. But last year, he ripped into Hillary Clinton aides repeatedly for exercising the same privilege during the congressional investigation into her private email server.

"The mob takes the Fifth," Trump told a campaign crowd in Iowa last September. "If you're innocent, why are you taking the Fifth Amendment?"

On the campaign trail, Donald Trump was not much of a fan of the Fifth Amendment.

Now, it's Trump's fired national security adviser, Michael Flynn, who is invoking the Fifth, hoping to avoid handing over documents to a Senate panel investigating Russia's meddling in the 2016 election.

The White House has so far kept quiet about Flynn's move. But Democrats are eagerly circulating Trump's past comments suggesting sinister motives for it.

"Trump previously declared that only people who are guilty invoke the Fifth Amendment," the Democratic National Committee said in an email including Trump's past quotes. It added that Trump had continued to defend Flynn even after firing the aide for lying about his contacts with Russia during the campaign.

Trump has veered back and forth on what it means to invoke the Fifth.

In 2014, then-businessman Trump had some free advice for Bill Cosby, who was facing a barrage of sexual assault accusations.

"If you are innocent, do not remain silent," Trump tweeted. "You look guilty as hell!"

But in 1998, back when Trump still was getting along with the Clintons, he suggested that Bill Clinton might have been better off to plead the Fifth during the investigation into his affair with Monica Lewinsky, saying, "I'm not even sure that he shouldn't have just gone in and taken the Fifth Amendment."

In 1990, during his divorce from first wife Ivana, Trump invoked the Fifth Amendment nearly 100 times, mostly "in response to questions about 'other women,'" according Wayne Barrett's biography "Trump: The Greatest Show on Earth."

Trump is far from the only politician to insinuate that invoking the Fifth is evidence of guilt when it's used by others.

When Sen. Joseph McCarthy was on a hunt for communist sympathizers in the 1950s, his committee pushed the idea that any witness who refused to testify was a "Fifth Amendment Communist."

McCarthy called the refusal to testify "the most positive proof obtainable that the witness is a Communist."

In 1986, when fired Reagan aide Oliver North invoked the Fifth in the Iran Contra scandal, Democratic Sen. John Glenn of Ohio unleashed withering criticism: "I can't think of anything that is going to polarize Capitol Hill more or make this into a political football any more than people taking the Fifth or stonewalling it and preventing all the information from coming out."

In 2013, then-Republican National Committee Chairman Reince Priebus, now Trump's chief of staff, said taking the Fifth was a sign that "there's clearly something serious the American people are not being told," when IRS official Lois Lerner refused to testify in an investigation into political bias in the Obama administration's treatment of tax exempt organizations.

Flynn's lawyer, in a letter to the Senate committee, said Flynn's decision to invoke his constitutional protection was not an admission of wrongdoing but rather a response to the current political climate, in which Democratic members of Congress are calling for his prosecution. Earlier, Flynn requested immunity in exchange for agreeing to cooperate with the committee.

Trump himself tweeted in March that Flynn should ask for immunity because he's facing "a witch hunt."

Last year, though, during the Clinton investigation, Flynn declared, "When you are given immunity, that means that you probably committed a crime."

Legal scholars are critical of those who try to taint others for invoking the Fifth, saying it clouds an important constitutional right and feeds into public misperceptions that taking the Fifth automatically suggests someone is guilty.

"This is a really important part of the Bill of Rights," said Emory Law Professor Mary Dudziak. "The idea that it's shameful to plead the Fifth is on some level deeply problematic and we should push back from that."

She added that in order for the right to work well, "it has to work in periods that seem not to be admirable as well as periods when we want people to be able to protect themselves."

James Duane, a professor at Regent University School of Law in Virginia, said invoking the Fifth isn't a sign of guilt or innocence but rather an indication that the person understands the risks that can come with testifying, even for someone who is innocent.

Politicians, he added, love to assume that that there's something sinister about other people invoking the Fifth, "but when the shoe's on the other foot, then they clam up in a heartbeat."

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