Billionaire Tom Steyer, one of the leading Democratic megadonors in the 2018 election cycle, suggested he could get involved in a Senate battle brewing in the red state of Texas.

In an exclusive interview with CNBC, the founder of nonprofit group NextGen America said he has not ruled out backing Rep. Beto O'Rourke, a Democrat, running against conservative Republican incumbent Sen. Ted Cruz.

"We are intrigued by Texas, and we are aware what we have to do in order to have an impact on a state that big. We need a lot of resources, but we have not made a decision to be involved with it," Steyer said.

The billionaire donor's consideration about jumping into the fray is the latest bit of intrigue in the race. O'Rourke is starting to creep up in the polls while raking in cash in his bid to defeat Cruz, who had sought the 2016 GOP presidential nomination. A Democrat hasn't held a U.S. Senate seat from Texas since 1993.

"The idea that Texas is even in play is sort of mind boggling," Steyer said.

A Quinnipiac poll from last week showed Cruz with a 3-point lead over O'Rourke, a difference that's within the margin of error. However, 53 percent of respondents said they did not yet know enough about the underdog Democrat to form an opinion of him.

O'Rourke has been winning in the fundraising battle.

He more than doubled the amount Cruz raised in the first quarter of 2018, bringing in $6.7 million. The Republican raised $3.2 million during that period.