At campaign stops, Cruz, a former presidential candidate who is seeking a second term in the Senate, has gone after O'Rourke as a "gun-grabbing liberal" and portrayed him as out-of-step with the bulk of Texas voters.
Cruz and O'Rourke faced off in their first debate ahead of November 6's congressional elections at Southern Methodist University in Dallas on Friday, and Cruz's strategy swiftly became clear: Paint O'Rourke as too radical for this traditionally Republican state.
"Thoughts and prayers are just not going to cut it anymore, Senator Cruz, the people of Texas deserve action", O'Rourke said. Most polls indicate the election is now too close to confidently predict.
The surprisingly competitive Senate race has become one of the most watched and talked-about contest of the 2018 midterms. Democrats need two more seats to gain control and upend President Donald Trump's agenda.
Friday night was the first debate for Cruz and O'Rourke.
O'Rourke in turn blasted Cruz for supporting massive deportations of illegal immigrants. That's a big deal in Texas, which hasn't elected a Democrat to statewide office since 1994.
At the same time, his campaign has kept the spotlight and money away from other races that are critical to Democrats' hopes of taking the Senate in states such as Nevada and Tennessee. He has complained that outside Democratic groups are providing O'Rourke with a fundraising advantage.
Sen. Ted Cruz speaks on a variety of topics at the Barn Door Steakhouse in Odessa, Texas, Aug. 25, 2018.
It's the first of three scheduled ahead of Election Day. Cruz wants to add more officers and metal detectors in schools.
O'Rourke said Cruz was trying "to mislead" the public. "I know that he's doing it for one reason".
On Twitter, both candidates' names trended as "Ted Cruz" tweets in the USA topped out at just shy of 70,000, while "Beto" tweets got to 132,000.
"The challenge for O'Rourke is to show that he is more than just a charisma candidate, that he's more than just a pretty face or an empty suit, that he really does have command of the policy issues", Wilson said.
During the debate, O'Rourke supported the rights of NFL players who have protested during the National Anthem, comparing them - as he did weeks ago in what became a viral video - to protesters in the civil rights movement.
"The high-velocity high-impact round from an AR-15 will blow a hole the size of an orange out your back", O'Rourke said.
In his closing statement at the debate, Cruz lumped O'Rourke in with NY congressional candidate Alexandria Ocasio-Cortez, an avowed socialist, and argued that he was to the left of progressive USA senators Bernie Sanders and Elizabeth Warren.
"I don't buy into the labels", he replied. Cruz appeared to be referring to O'Rourke previously suggesting that inherent biases in the criminal justice system promote racism.