A Quinnipiac University Poll found that Cruz was leading O'Rourke by five points, with 3 percent of Texan voters still undecided.
"It is time to take bold steps forward," The Dallas Morning News editorial board wrote.
Trump's campaign said 100,000 people requested tickets for Monday's rally for Senator Ted Cruz.
Donald Trump has changed his tune on Republican Senator Ted Cruz since the 2016 election.
"That wasn't the best phrase for me to use," said O'Rourke in an interview with ABC News that aired Sunday. "I'm going to do my best to stay focused on the future."
The panel said Ted Cruz had been forced to "bend the knee" and submit to President Trump as they put past insults behind them before tonight's Houston rally.
"I don't know that it makes any sense to respond," Beto O'Rourke said.
"You think that putting a sexual assaulter on the court is a victory for women?" a protester asked Texas Republican Senator Ted Cruz over his vote to confirm Brett Kavanaugh to the Supreme Court.
A former Trump campaign data strategist claimed Texas Democratic Senate candidate Beto O'Rourke is liked by journalists because he's a "beta male" with "metrosexual" tendencies.
"There is a loss of civility, there is an anger, there is a rage on the far left that is frightening," the senator said. "The images of the left-wing mob beating on the doors of the Supreme Court—that's not good for the country."
"Senator Cruz is not going to be honest with you... He's dishonest. It's why the president called him 'Lyin' Ted,' and it's why the nickname stuck. Because it's true," O'Rourke said during the second Texas senatorial debate.
Beto O'Rourke announced a staggering fundraising total, but continues to trail Ted Cruz in the polls.
Trump's rally for Texas Senator Ted Cruz will be held at NRG Arena, which has only 8,000 seats, while the largest stadium in Texas has close to 103,000 seats.
A new CNN poll found Monday that Texas Senate hopeful Beto O'Rourke was listed as a top 10 candidate for the Democratic presidential nomination in 2020.
Polls last month had offered a major boost to Beto O'Rourke's hopes, but that was before the Kavanaugh Supreme Court nomination fight.
"I am so grateful to him for his service; he's going to go down as one of the greatest presidents. And yet, this [election] is on Texas," said O'Rourke.
"I'm, like, Wow, that's a pretty extreme position, if you're Bill de Blasio," Trump Jr. said, referring to New York City's mayor.
The Texas Senate candidate said he knew the comments were disrespectful.
The senator was recently heckled out of a restaurant in Washington, D.C.
"The biggest gun we've got is called the ballot box. If you don't like who's in there, vote 'em out," sang the country music legend.
Democratic U.S. Senate candidate Beto O'Rourke of Texas, with help from Willie Nelson and other country singers, hosted the largest single-candidate political rally in the country at least since the 2016 presidential election.
Days after protesters in D.C. bum-rushed Sen. Ted Cruz at a D.C. restaurant, the owner announced that he, his staff and their families are being targeted with "life-threatening messages."
Senator Ted Cruz (R-Texas) appears to have been keeping a close eye on his competition.
The Republican and his wife left the Italian restaurant after a crowd entered and began chanting.
O'Rourke complimented Cruz's dedication to his country and thanked him for sacrificing time with his family in order to stand for his beliefs and goals. Cruz took the opportunity to repeatedly compare O'Rourke to Senator Bernie Sanders and to say that he was fighting for socialism.