CHARLESTON, S.C. (Reuters) - Republican activists in South Carolina are urging party voters to do the seemingly unthinkable: support U.S. Senator Bernie Sanders’ bid for the White House in the state’s Democratic primary on Saturday.

The unusual effort is aimed at exposing what the activists see as flaws in the Southern state’s open primary system - and at boosting the candidate many Republicans view as the easiest rival for Republican President Donald Trump to beat in November.

Sanders enters Saturday’s contest as the front-runner for the Democratic nomination, fueled by wins in New Hampshire and Nevada and a near-tie for first in Iowa.

But the Vermonter, an independent who calls himself a democratic socialist, now faces a tough challenge from Joe Biden. The former vice president is bolstered by strong support from African Americans who comprise a large share of South Carolina’s Democratic electorate.

“Bernie is a socialist and the most egregious of all the candidates. He is also the weakest against Trump,” said Pressley Stutts, a Tea Party activist and one of the organizers behind an interference effort dubbed “Operation Chaos.”

The Sanders campaign did not respond to requests for comment.

Democrats and Republicans previously have threatened to interfere with the other party’s primary process in South Carolina and elsewhere, generally without success. In Iowa, however, Republicans boasted they clogged Democratic Party telephone lines, exacerbating embarrassing delays in reporting caucus results.

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State Democratic Party Chairman Trav Robertson called the Republican efforts “nonsense.” He said party leaders expect greater Democratic primary numbers not due to Republican gamesmanship but because voters are fed up with the “immoral, anti-Christian” person occupying the White House.

South Carolina voters do not register by party and are allowed to vote in either party’s contest. After the state Republican Party canceled its primary this year out of deference to Trump, activists long angered by Democrats allegedly participating in local Republican votes saw an opportunity for payback.

Stutts said he has been inundated with emails, texts and social media messages from Republicans eager to join the effort. On Tuesday, he held a news conference in Greenville, South Carolina, to announce the plan to vote for Sanders after some internal wrangling over which candidate to support.

Karen Martin, a freelance editor and pet sitter in Spartanburg, is leading a similar effort she has coined “Trump 2-29” in a nod to the primary date. Like Stutts, she wants the state to change to a closed primary system and sees delivering a victory for Sanders as the best way to antagonize a Democratic Party that includes some who are reluctant to embrace his candidacy.

With no party registration figures, it will be difficult to measure the impact of the Republican organizing efforts.

A Public Policy Polling survey released on Monday found a “fair number” of Trump supporters planned to vote in the Democratic primary. But the survey said their dispersed support among several candidates meant they would not be a factor.

State Republican Party Chairman Drew McKissick said his organization has not endorsed the activists’ efforts, nor has it called for the movement to stop.

“I am not sure exactly how much this will move the needle,” he said. “I do know that I’m having fun watching the Democratic circus and that Bernie Sanders, a socialist, would provide the ultimate contrast between the two parties.”