From Democratic firm Public Policy Polling:

David Dewhurst leads Ted Cruz 46-29 in the Texas Republican Senate primary and the main question on Tuesday will be whether he can sneak over 50% and avoid a runoff. Tom Leppert’s in third at 15% with Craig James at 3% and 2% of voters preferring someone else. 5% remain undecided and if Dewhurst can pick up enough of those folks it might get him over the finish line.
Dewhurst’s 17 point lead represents a reversal of the direction the race had been heading in. Dewhurst started out with a 29 point lead in our polling last September but by January that had declined to 18 points and on our last poll, a month ago, it was down to 12. But Cruz has only gained 3 points over the last four weeks, while Dewhurst has seen an 8 point bump in his support.

Cruz’s campaign has been pushing hard to keep Dewhurst below 50 percent so Cruz can face him directly in a runoff.