DeLay has represented his district since 1984 and is accustomed to rolling up big victories. He got 60 percent of the vote in 2000 and 63 percent two years ago.
He is expected to win again this year, but not as handily as in the past.
"I think at the end of the day, Tom DeLay will win. But his margin of victory will be much smaller than usual," said St. Thomas University political scientist Jean-Philippe Faletta.
Based on some polls, there is a possibility DeLay could get less than 50 percent of the vote because the ballot also includes a strong independent candidate and a Libertarian.
University of Houston political scientist Richard Murray believes DeLay is running hard because he fears a narrow win could weaken him in Congress.
"His constituency is the Republicans in Washington," he said. "If they see him as being damaged here in Texas on top of other things -- it would not be good for the Majority Leader to just get a plurality win in his home district."