DALLAS (CBSDFW.COM) – While Democrat Rep. Beto O’Rourke is attracting big crowds and raising record amounts of money, $38.1 million in the last three months, Republican Sen. Ted Cruz is still leading in the latest polls by nine points.

SMU political science professor Cal Jillson said Friday, Rep. Beto O’Rourke must sharpen his advertising against Sen. Ted Cruz and stop playing Mr. Nice-Guy.

Beto O’Rourke (CBS11)

Jillson said O’Rourke can still regain momentum.

“He’s going to have to rethink his advertising campaign,” said Jillson.

Jillson says O’Rourke must explain to voters why Texas would be better off with him as Senator than Cruz, something Jillson says O’Rourke has not done.

“O’Rourke has been unwilling to do the negative stuff, but I don’t think you can just leave it out, even if you’re running a positive campaign, you still have to challenge the guy whose job you want.”

O’Rourke tells supporters he doesn’t like going negative, and in his latest TV ad, he says he doesn’t want to play to people’s fears.

“I’m confident that when we see each other not as Democrats or Republicans, but as Texans, Americans, and human beings, there’s no stopping us,” O’Rourke says in the ad.

During his rally in Plano last week, Cruz mocked O’Rourke’s ads.

“They’re all about rainbows and puppies and hugging kids,” said Sen. Cruz. “So yeah, he may open up the borders, destroy our economy, make our homes less safe and fundamentally weaken Texas, but he’ll hug a kid.”

US Senator Ted Cruz (JIM WATSON/AFP/Getty Images)

As for Cruz, his ads regularly attack O’Rourke’s positions.

“Ted Cruz is leading the fight for the Texas oil and gas industry, but Beto O’Rourke is no friend of Texas energy,” says one Cruz ad.

At his rally Thursday night in McKinney, O’Rourke mocked Cruz’s negative ads.

“The grainy photo of Beto O’Rourke, veins popping out of his neck, coming to get you and your family, do these terrible things for Texas,” O’Rourke said.

Professor Jillson said in the last couple of weeks before Election Day, Sen. Cruz will likely run ads about his priorities if he’s reelected.

He said that’s typical of most campaigns — but O’Rourke’s campaign is not typical — he has said he doesn’t use any consultants.