Cruz is beyond safe, Democrats are never wining Texas anytime soon because the states black and Hispanic communities never show up to vote and the states white population is overwhelmingly evangelical, rural, and conservative.
Describing Texas' population as overwhelmingly rural is...amazingly misguided. Stunningly so.
The GOP base in Texas isn't rural West Texas or rural East Texas, it's the rich Dallas and Houston suburbs.
As of 2010, 84.7% of Texans live in a place defined by the Census Bureau as urban or suburban and only 15.3% in rural areas. I imagine that gap has only gotten bigger in the seven years since.
The path to a Democratic Senate win in Texas is replicating the suburban swings we've been seeing and cranking up Democratic turnout in the major cities to 2016 Presidential levels.
Yes, I really think it will be one of these 2 scenarios at the end of the day:
1. Cruz maintains Romney's margins in the suburbs, loses only modest ground in the cities themselves and wins by 10-15.
2. O'Rourke continues the 2016 trends even further, flips Tarrant, wins the narrow Clinton suburban districts TX-07 and TX-32 by 10-15% and barely flips TX-21 and/or TX-02 to create a < 3% race either way statewide. This would be the Dem wave equivalent of Warner vs. Gillespie 2014, maybe even Gardner vs. Udall if O'Rourke can thread the needle.
So I would rate it Lean R right now, but I really think it will be either Safe R or a Tossup by next November.
Cruz won by 15 in 2012 against a some dude. So him matching that performance is nearly inconceivable, short of O'Rourke being a pedophile.