BOR and QR report on an internal poll done by the Joan Huffman campaign for SD17. I happen to have the press release about the poll, so let me quote the relevant bits:

The Joan Huffman Campaign released today internal poll results showing that voters prefer Huffman by a 3-to-1 margin over the other Republicans in the race for State Senate District 17 while 2/3 of voters either do not know or have a negative opinion of Chris Bell, the leading Democrat.

Four Republicans and two Democrats are campaigning in a Special Election for the vacancy left by Kyle Janek. Joan Huffman leads the Republican pack with 12% of registered voters, while her next closest competitor lags behind with only 4% support. Bell had support from 41% of registered voters. "This poll verifies it's a two-person race," said Huffman Campaign Manager, Jessica Colón. "Although the leading Democrat, Chris Bell's high negatives indicate his support is soft and will become softer once voters are reminded of the specific reason they have a negative impression of him."

[...]

The Texas Polling Group conducted a Senate District 17 survey August 27-29. The overall sample included 500 randomly chosen registered voters throughout Senate District 17 with a margin of error of ±4.5% at a 95% confidence level. 31% percent polled had a Democrat Primary vote history, 24% a Republican Primary Vote history, 8% a mixed Primary vote history, and 37% an exclusive general election vote history. When asked how they would vote in the upcoming special election, voters responded as follows: 41% Bell; 12% Huffman; 4% Furse; 3% Harpold; 41% Undecided. Democratic candidate Stephanie Simmons and Republican candidate Ken Sherman were not included in the poll.

Obviously, there's a lot of undecided voters in these samples. The hope on the Republican side is that a large number of those voters will go GOP, they just haven't figured out for whom yet. Of course, it may be that enough of them don't vote in this race to boost Bell past 50% even if his absolute level of support doesn't increase. One way of looking at this result is to say that among voters who expressed a preference, Bell had nearly 70% of them. If this is an accurate picture, and you assume all of the undecideds do vote, Bell needs a bit more than 20% of them to choose him to win outright. If only three-quarters of them vote, he needs less than 15% support from them. His task is far from insurmountable.

And if it does go to a runoff? I would of course rather it didn't, but I would still feel pretty good about Bell's chances if it did. Runoffs are about getting the folks who voted for you the first time to come back and do it again. Better to start out with a lead than not. No guarantees, of course - look at Al Edwards and Henry Bonilla from 2006 for two such examples - but it's the position you want to be in if you have to be there at all.