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At a campaign event for Donald J. Trump in Mississippi last weekend, Lynette Hardaway and Rochelle Richardson — two African-American YouTube stars who go by the names Diamond and Silk — rallied the roaring crowd with a plea. “Ditch and switch! Ditch and switch!” they yelled.

The pitch was directed at Democrats and independents in the audience, urging them to become Republicans and vote for Mr. Trump if they really want to show their support.

It could be an important strategy for Mr. Trump as the pace of primary season picks up, and he looks to turn his raucous campaign events into voters, delegates and ultimately the Republican nomination. To accomplish that, Mr. Trump will be relying on people who do not tend to vote and trying to persuade some Democrats and independents to change parties so that they can vote in states that allow only registered Republicans to participate.

Ms. Hardaway and Ms. Richardson are former Democrats who became supporters of Mr. Trump and jumped to the Republican Party in North Carolina in September. While they are not formally affiliated with the campaign or paid by it, they have been urging other supporters of Mr. Trump to follow suit on social media and at rallies. They have even created a “ditch and switch” website explaining to voters which states are closed primaries and when the deadlines are for changing party affiliations.

“Donald Trump is going to have Democrats switching in droves to vote for him,” Ms. Hardaway said in an interview. “He’s going to be the only candidate to be able to pull independents and Democrats to vote for him in the primaries and the general election.”

Supporters of Mr. Trump have been spreading the word on Twitter that they have been switching parties and have been urging others to do the same.

“I would love to see more Democrats vote Republican in this election,” said Sunny Kreis Collins, a supporter of Mr. Trump from California who was urging people online to switch parties and vote for him. “The country is a mess.”

An analysis by The Upshot last week showed that Mr. Trump is popular with registered Democrats who identify as Republican leaners, drawing 43 percent of their support. What is more, his best states are those with traditions of Democrats who vote Republican in presidential elections.

Perhaps aware of this dynamic, Mr. Trump expressed outrage at Virginia lawmakers last month who introduced a requirement that Republican voters sign statements of affiliation on their primary ballots. Arguing that it was disenfranchising new voters, Mr. Trump called the move a “suicidal” mistake.

Despite the push by his supporters to get Democrats to change parties, the Trump campaign said that it was not making an organized effort to convert voters.

“It’s happening organically,” said Hope Hicks, a spokeswoman for Mr. Trump.