Republican presidential nominee Donald Trump's poll numbers continue to plunge, so the candidate is using his last days on the campaign trail to instruct supporters to monitor polling places for "election rigging."

Critics say such monitoring could be tantamount to illegal voter intimidation and deliberately targets minority and young voters.

Trump began recruiting so-called election observers online in mid-August, soon after another series of grim, unfavorable polls. His campaign's website spurred concerns about intimidating minority voters as the effort was announced. Those anxieties have recently resurfaced and heightened, The New York Times reported.

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Trump's "election observers" might constitute a violation of a 1982 consent decree, election law expert Rick Hasen told The Washington Post.

"If I were the lawyer for the [Democratic National Committee], I would try to make the case that Trump is acting as an agent for the RNC, and the RNC is acting as an agent of Trump, since they have a joint fundraising committee, and they are working together," Hasen said. "I can't tell you how a court would rule on this question, but I certainly think the Democrats could make that case."

Individual "election observers" could potentially face civil and criminal charges related to voter intimidation — which can result in up to a year in prison, Think Progress reported.

(We'll discuss the consent decree a bit later in this story.)

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Trump's calls for election observers are nothing new.

So-called "election observers" cropped up during the rise of the Tea Party. Critics said they were nothing more than goons recruited to intimidate voters, particularly those of color.

The King Street Patriots, a Texas-based Tea Party group, spawned the voter monitoring organization True the Vote in 2009, Colorlines reported. True the Vote sprang into action during the 2010 midterm elections with an initiative that allegedly targeted Black and Hispanic neighborhoods in Houston. The group's activity prompted an investigation from the Harris County Attorney's office in Texas, The Atlantic reported.

From The Atlantic:

"Under the banner of an offshoot organization called True the Vote, the Patriots dispatched hundreds of observers to minority neighborhoods in and around Houston, where they gathered more than 800 complaints of improper voting. Their efforts made national headlines, and phone calls and emails began pouring in from activists around the country who wanted to join the cause.

"With a presidential election looming, [founder Catherine Engelbrecht] decided that it was time to take the fight nationwide. Last year, at True the Vote’s first annual summit, she urged attendees to carry the mantle of 'voter integrity' back to their home regions by forming spinoff groups."

True the Vote's election observers also allegedly harassed student voters in Wisconsin during the unsuccessful recall election of GOP Gov. Scott Walker in 2012.

Wisconsin's Government Accountability Board answered voters complaints in the following statement: "In recent elections we have received disturbing reports and complaints about unacceptable, illegal behavior by observers. Voters expect a calm setting in which to exercise their right to vote."

True the Vote also been busy this year.

True the Vote, for its part, maintains that the group isn't engaging in foul play.

"Contrary to popular belief, TTV does not have the authority to place poll watchers anywhere in the vast majority of states," TTV spokesperson Logan Churchwell told ATTN: via email. "We train poll watchers to not speak with voters, even if some states allow it in specific situations. We also do not train, encourage, or condone informal observers to operate outside of the protected polling locations."

Voter intimidation also colored Republican political efforts during the 1980s.

From The Nation:

"In 1981, during a New Jersey gubernatorial election, the Republican National Committee launched a 'Ballot Security Task Force' that sent sample ballots to voters in predominantly African-American and Hispanic precincts. When 45,000 letters were returned as undeliverable, the RNC tried to remove the voters from the rolls and hired off-duty cops to patrol polling sites in Black and Hispanic neighborhoods of Newark and Trenton. Police carried firearms at polling places and wore armbands reading 'National Ballot Security Task Force,' while the RNC posted large signs saying, 'THIS AREA IS BEING PATROLLED BY THE NATIONAL BALLOT SECURITY TASK FORCE. IT IS A CRIME TO FALSIFY A BALLOT OR TO VIOLATE ELECTION LAWS.'

"After the election, the Democratic National Committee won a court settlement ordering the RNC to 'refrain from undertaking any ballot security activities.'

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The Republican National Committee was forced in 1982 to enter into a consent decree with the Democratic National Committee addressing "ballot security" initiatives.

That was clarified in a 1987 decision by the Third U.S. Circuit Court of Appeals in Philadelphia, which covers Delaware, New Jersey, Pennsylvania, and the Virgin Islands.

The RNC has since disputed the decree numerous times, without success.

A loophole?

The 1982 ruling concerned programs that came directly from the RNC. True the Vote's ballot monitoring, meanwhile, technically does not (that would be illegal). True the Vote claims to be a nonpartisan voting rights organization.

You can read a comprehensive history of voter intimidation in U.S. politics courtesy of the liberal advocacy and research group People for the American Way.

ATTN: reached out to the Trump campaign to comment on this story and will update it when we receive a response.