More opposition helps Graham. He is already pretty assured to be the top vote getter in the primary, but probably not 50%. He can sit on most of his money and watch his challengers go at it, spending what little money they have for the campaign. If there is a run-off, he will have about 50 times the cash as his opponent, allowing him to dominate the TV and radio.
Another possibility is the opponents beat up on each other to a point they look weak, Graham pumps in big money the last two weeks before the primary Election Day and captures more than 50% of the vote.
Either way, with a large field, I see no way Graham is defeated next year by a republican.
Dewhurst had a lot more money than Cruz, plus GOP-E support. Dewhurst was the top vote getter in the primary but didn't get 50%. When it came down to the run-off, money flowed to Cruz. Then Cruz beat him like a red-headed step child over conservative issues.
/johnny