"It's clear Congressman O'Rourke's pollsters have told him to come out on the attack", Cruz said.
Ted Cruz is the butt of another joke, this time it's an ad aimed at the senator's appreciation for the fast food joint, White Castle, instead of Texas' Whataburger.
"He's dishonest. It's why the president called him "Lyin" Ted, ' and it's why the nickname stuck, because it's true", said the three-term congressman from El Paso, who is trailing the GOP incumbent in the polls.
Cruz fired back, telling O'Rourke his universal health care plans didn't make sense even using "elementary school math" and alluded to his declining odds at the polls.
It was a change in strategy for O'Rourke, who has been hesitant to attack Cruz while portraying himself as a figure who could bring Texans together.
O'Rourke also faulted Cruz for leading the 2013 federal government shutdown, for missing votes in Washington and for campaigning in Iowa to further his presidential ambitions rather than spending more time in Texas.
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Earlier, emergency officials said the explosion was believed to have been caused by a gas canister explosion. Reuters news agency said the schools and pre-schools were being evacuated in the city after the blast.
He also noted that his monster fundraising has come without accepting donations from outside political groups, but Cruz said O'Rourke still 'goes with the left-wing national activists and left-wing national donors'.
"If you have this special relationship with President Trump, then where is the result of that?" No Democrat has won any of Texas' almost 30 statewide offices since 1994, the nation's longest political losing streak. "He's dishonest", O'Rourke said.
"Ted Cruz is for Ted Cruz", he said, adding the senator's re-election campaign was "based on fear".
O'Rourke, an El Paso congressman, has used record-setting fundraising and a background as a one-time punk rocker to attract heaps of national attention as he tries to upset Cruz and become the first Democrat to win statewide office in Texas since 1994. O'Rourke and most Democrats opposed the measure.
O'Rourke said there needed to be a greater focus on screening methods for people entering the country, and hit Cruz for his vote against a permanent solution for Dreamers, recipients of the Deferred Action for Childhood Arrivals program.
"Really interesting to hear you talk about a partisan circus after your last six years in the U.S. Senate", O'Rourke said to laughter in the audience. But Cruz has more recently opened up around 10-point leads.
Cue a clip of Cruz declaring that "I'm a big fan of eating White Castle burgers".