If Kasich finishes second Bush third and Cruz fourth (or fifth) going into South Carolina where Kasich would have little support, the last poll has him on 1%, the situation would seem ideal for Trump
Kasich would of course get massive media coverage. which has started already with this huge puff piece
"The transformation of John Kasich"
And the MSM. particularly Fox would be 24/7 "Kasich surges" as they discard "Cruz surges' and to a lesser degree "Rubio surges."
All this puffery would give Kasich some momentum going into South Carolina but I can't see him appealing to the voters there especially if Trump comes out of New Hampshire with a solid win.
The longer Kasich stays in the race the better for Trump who can keep hammering at Cruz on his right whilst Kasich can hammer at Rubio on his left.
At this point it doesn't seem feasible for Kasich to win the Nevada caucus and the Florida primary, but he can hold down Rubio and Bush's support which would leave Trump in a very strong position to keep rolling up pluralities in state after state.
Trump's opponents may be one state wonders, Cruz in Iowa, Kasich (2nd) in New Hampshire and possibly 1st in Ohio.
This is where Trump's nationwide poll lead, which has been discounted by pundits, may actually be the pointer to his final success as his support is broad whilst others is narrow.