First, there was the buzz. O'Rourke gave up a comfy El Paso-area congressional seat to challenge a guy who came close to winning the Republican nomination for president. Liberal activists were intrigued by O'Rourke's savvy social media campaign.
Then, there was the fundraising. O'Rourke quickly became a darling on the left and has out-fundraised Cruz nearly continuously the past few quarters, despite rejecting money from outside political groups.
Earlier this month, O'Rourke announced that he had collected $6.7 million in donations through the first three months of 2018. That number is huge for any Senate candidate but especially for a Democrat in Texas. Cruz said he raised less than half of that — $3.2 million — in the same period.
And now, there are the polls. On Wednesday, Quinnipiac University published the first independent, high-quality poll in the race. They found that right now, the race is too close to call. Cruz is ahead by three points, but it's within the margin of error of plus or minus 3.6 percentage points.
It all adds up to this possibility: Could a Democrat win a Senate race in Texas this year?
That's no small question. Unseating a Texas senator is one of the hardest things to do in politics. No Democrat has won a statewide race in Texas in 24 years, which the Associated Press says is the nation's longest losing streak.
But some Democrats say the puzzle pieces are coming together to give O'Rourke a better chance than any other Democrat who has come before him.
“Considering this cycle that Democrats won in Alabama, Western Pennsylvania and local districts around the country that are more challenging then Texas, it makes sense that this race would be close,” said Adam Bozzi of End Citizens United PAC, which endorsed O'Rourke because he rejected money from outside political groups. Bozzi said his group's internal polling shows O'Rourke has been within single digits of Cruz all this year.
O'Rourke has far from a perfect runway in Texas, even in a year where Republicans across the nation are warning of the potential for a blue wave. In last month's Texas primary elections, 1 million Democrats voted, nearly 100 percent higher turnout than in 2014. But 1.5 million Republicans voted in that same primary, and Cruz got more than twice as many votes as O'Rourke did.
In that primary, O'Rourke didn't have a particularly strong performance for a candidate campaigning to take out one of the most well-known politicians in the state. He ceded 38 percentage points to two much lesser-known, less-hyped challengers. He lost counties in the south, east and panhandle.
Democrats say O'Rourke simply has a name-recognition problem. In the Quinnipiac poll, 53 percent of Texas voters say they hadn't heard enough of O'Rourke to know whether they like him. He hails from the far western corner of the state and needs time to introduce himself. He's certainly got the money to do that.
Republicans are heartened that Cruz polls ahead of O'Rourke on doing a better job of handling the economy, taxes and health care. But O'Rourke could make up those gaps by winning over the sizable chunk of voters who say they don't know which candidate is better.
This is just one poll, a snapshot in time. It means that if the election were held seven months early, the race might be too close to call and, remarkably, Cruz could be in trouble.
A lot can and will likely change between now and then. One big potential change to watch: It's not clear whether the registered voters who were polled will be the ones to show up in November. Republicans traditionally vote in midterm elections in much higher numbers than do Democrats, especially in Texas. And some Democrats are warning this poll may be too good to be true: "At this point, we should be skeptical of the notion that Cruz is on the brink of defeat,” wrote left-leaning blog Daily Kos.
But at the very least, a Texas Democrat is presenting the most serious challenge to a Republican senator in years. For Senate Republicans in Washington, who are also trying to defend seats in Nevada, Arizona and Tennessee, and hang onto their 51-49 majority, a competitive Senate race in Texas is last thing they want to hear about.