The chart above is from the Morning Consult Poll. It compares the support of the major candidates both before and after the South Carolina primary. The pre-S.C. primary poll was done between February 23rd and 27th of a national sample of 13,428 likely Democratic primary voters, and has a 1 point margin of error. The post-S.C. poll was donjon March 1st of a national sample of 2,656 likely Democratic primary voters, and has a 2 point margin of error.
The poll shows Joe Biden got a significant 7 point boost after his victory in South Carolina. He polled 19% before that primary and 26% after it.
Bernie Sanders is still leading in the poll with 29%, but his lead has narrowed. He led by 13 points before the primary. That dropped to a 3 point lead after the primary.