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New data: Donald Trump loses support ahead of South Carolina primary

As South Carolina voters head to the polls Saturday to cast ballots in the GOP presidential primary, new survey data suggests the race has shifted in the final week, with GOP frontrunner Donald Trump losing some support in the state.

When our CBS News/YouGov Battleground Tracker polled South Carolina Republicans between February 10-12, 2016, our results for the presidential primary put Donald Trump on top with the support of 42 percent of likely primary voters. Texas Sen. Ted Cruz came in second with 20 percent, and Florida Sen. Marco Rubio came in third with 15 percent. Ohio Gov. John Kasich was at 9 percent, and former Florida Gov. Jeb Bush was at 6 percent.

CBS News and YouGov were able to re-contact 262 of the respondents on Friday, and the results showed a discernible movement away from Trump. Only 84 percent of Trump voters said that they were still planning on voting for him, with 4 percent saying they now planned to vote for Cruz and 4 percent saying they now intended to vote for Rubio.

Ninety-one percent of the former Cruz voters say they still plan to vote for him, but 5 percent now intend to vote for Rubio, and 2 percent say they will vote for Trump.

Of Rubio's supporters, 82 percent are still planning on voting for him, but 8 percent now intend to vote for Cruz and 4 percent plan to vote for Trump.

The Florida senator has been strengthened overall, however, by defectors from Bush and Kasich. Only 68 percent of former Kasich supporters still intend to vote for him, while 26 percent now support Rubio, and 5 support Cruz. Bush retained only 58 percent of his voters from last week. Thirty-three percent now say they are in Rubio's camp, and 8 percent say they'll vote for Cruz. Neither Kasich nor Bush absorbed significant support from their rivals.

If we apply these switch rates to our previous results, here is how we would now estimate the vote split in Saturday's primary:

Donald Trump -- 36 percent

Ted Cruz -- 22 percent

Marco Rubio -- 21 percent

John Kasich -- 8 percent

Jeb Bush -- 4 percent

Other -- 7 percent

These new estimates, as mentioned previously, are based upon small samples, not a full Battleground Tracker survey. They suggest Trump is still headed for a clean win in the state, but not as big a victory as we anticipated a week ago.