O'Rourke responded by evoking a moniker Donald Trump bestowed on the senator when the pair were bitter rivals during the 2016 Republican presidential primary. Ted Cruz (R-Texas) as dishonest and overly ambitious in the two candidates' second debate Tuesday night, striking a new tone for a progressive campaign known for its unrelenting positivity.
"He's dishonest", O'Rourke said. "That's why the president called him Lyin' Ted and it's why the nickname stuck because it's true".
Cruz laughed it off and tried to turn attention back to polls that show the Democrat falling behind the Republican.
Cruz said. "With Congressman O'Rourke leading the way, [there'll be] two years of a partisan circus and a witch hunt on the president".
Trump referred to his then-presidential opponent Cruz as "Lyin' Cruz" repeatedly during his 2016 campaign.
O'Rourke criticized Trump for alienating trade partners like Canada and Mexico, and said his trade war is "hurting no state more than it's hurting Texas".
Even if O'Rourke were to lose by that margin, however, it would represent a major gain for Texas Democrats.
In a line that underscored Democratic worries that O'Rourke hasn't won over enough Latino voters, Cruz said: "The people of Texas, and I will say, especially the Hispanic community, we don't want to see taxpayer-funded, Medicaid-funded abortions".
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'.
O'Rourke's position on impeaching the president apparently has changed during the campaign. He ends with a quip about Cruz's Canadian origins and a final, "C'mon, Ted".
O'Rourke, who is giving up his El Paso congressional seat to challenge Cruz, shattered Senate fundraising records with any eye-popping $38-plus million in the three-month period through September. O'Rourke's response: "It's really interesting to hear you talk about a partisan circus, after your last six years in the US Senate".
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. "But I'll tell you what, traveling the state of Texas, meeting people regardless of their walk of life, their background, their party affiliation, you have inspired me".
Cue a clip of Cruz declaring that "I'm a big fan of eating White Castle burgers".