United States presidential election, 2016
There are two new polls out this morning on the South Carolina primary and the reflect the trend that we've been seeing earlier in the week. Let's go to the topline:

Poll: South Carolina House GOP Caucus
Sample: 1700 Likely voters
Margin of Error: 2.4
Trump 34, Cruz 16, Rubio 15, Bush 15, Kasich 8, Carson 7.

Poll: American Research Group (ARG)
Sample: 400 Likely voters
Margin of Error: 5.0
Trump 33, Cruz 14, Rubio 16, Bush 9, Kasich 14, Carson 3.

If you recall, yesterday's PPP poll (yes, you can laugh) had Trump 35, Cruz 18, Rubio 18, Bush 7, Kasich 10, and Carson 7.

To the extent these polls are reliable, we see that Trump has a clear lead, though his support has softened over the past couple of weeks. The question that we don't know, given Trump's lack of a ground operation, is the extent to which his voters will turn out. In New Hampshire we saw that Trump's supporters did show up to vote. But South Carolina is not New Hampshire. In 2012, South Carolina's turnout was 14 points below New Hampshire's in the primary and general elections. Likewise, for the 2014 off year election. I think we can consider any result for Trump below 30 has a huge defeat but smart money says he polls very close to 33.
The real battle is for second place but it is very high stakes and a bad throw of the die sees one or two candidates leaving the race within two weeks. This is the way I see it:

Cruz

Cruz probably finishes in second but not by a huge margin. Of all the candidate, Cruz is best positioned to be able to suck up a third place finish. His primary strength has always been Super Tuesday. Second place though, in a state where most of the elected officials are supporting someone else is a show of organizational strength.

Rubio

Rubio really needs a second place finish. If Rubio finishes third he staggers on but his electability becomes an issue. If he finishes fourth, his campaign is essentially over. Finishing 3-4-3 in the first three primaries does not build donor confidence. Finishing 3-4-4 says he can't win.

Bush

A second place finish by Bush gives him a huge new lease on life and does something to remove the odor of flopsweat from his campaign. All evidence indicates that his campaign is running on fumes. His Right to Rise PAC pulled $3 million in advertising buys for Super Tuesday indicating that it has thrown everything it has into South Carolina. Third or fourth place sees Bush out of the race within a couple of weeks.

Kasich

I find it hard to credit ARG's result showing Kasich in the scrum for second place but he did surprise in New Hampshire.

Carson

Carson is unaffected by South Carolina because he's running a mailing list operation, not a campaign.