Updated Thursday, Oct. 10, 2019, at 7:20 p.m. with Sen. Pat Fallon’s announcement that he would not be running against U.S. Sen. John Cornyn, R-Texas.

AUSTIN — Pat Fallon will not challenge fellow Republican John Cornyn for his seat in the U.S. Senate.

Fallon, a state senator who represents a large swath of North Texas, including parts of Denton, Sherman and Wichita Falls, told The Dallas Morning News in September that he was seriously considering challenging Cornyn in the Republican primary next year.

After a month of mulling the idea, Fallon told The News he had decided not to run because he wanted to be around for his kids — and because of fundraising issues.

“With our sons being 13 and 10, Susan was very concerned about how much time I would be away campaigning and, God forbid [her words!] I actually won, she was fearful that I’d miss the remaining half of the boys’ formative years,” Fallon said in a text message that he then posted on his Facebook page. “That and we were shy about $6 million that we would have needed as a bare minimum to be competitive for the GOP nomination!”

“A statewide US Senate race right now is simply not something that fits with the chapter in life that we’re in. I do plan on playing a role and do everything I can, whether that be as a volunteer or candidate in the future, to KEEP TEXAS RED!”

A staunch conservative who last year authored a bill to make it more difficult to remove Confederate and other historical monuments, Fallon has disagreed with many of Cornyn’s policy stances and questioned the longtime incumbent Republican’s conservative bonafides.

“Republican voters deserve a viable candidate who will better represent their values,” Fallon, R-Prosper, said in September. “We need someone new.”

Officials at Cornyn’s campaign had declined to comment on Fallon’s move to explore a Senate primary campaign. But the campaign sent out a fundraising appeal with a video of Cornyn’s endorsements, including Sen. Ted Cruz, Gov. Greg Abbott and Lt. Gov. Dan Patrick.

The next day, the Cornyn campaign sent The News an email with comments that conservative radio show host Mark Davis made about the announcement.

“Cornyn is going to be the nominee. That is a one hundred percent certainty. Because of that, any distraction, sideshow, diversion of money, passion, internecine squabbling is a waste of time away from what we must be focusing on,” Davis said at the time, according to the campaign. "It is about you, Pat. It is. You’ve got a bunch of people tell you that you that they think you can beat Cornyn, and you can’t. I love you enough to try to talk you out of this fool’s errand.

“Put down that crack pipe. ... Don’t do this.”

Speaking to The News in September, Former Dallas County Republican Party chairman Jonathan Neerman, a friend of Fallon, said the state senator has “always been a smart candidate and a smart campaigner.”

But Neerman said running a statewide campaign against a longtime incumbent would be tough.

"It's a lot different raising money in a state campaign than it is raising money in a federal campaign," Neerman said. "And I don't know how strong Pat's name recognition is beyond North Texas."

Neerman said a potential Fallon challenge of Cornyn would have gone against the GOP script for 2020, when primary challenges have been discouraged in favor of focusing on meeting the Democratic Party challenge.

"If we have an unnecessarily damaged candidate coming out of the primary, that won't meet the objective of running in November and beating Democrats," Neerman said.

Cornyn, 67, is seeking a fourth six-year term. He had seven primary challengers in 2014 and won without a runoff. For 2020, he has two other challengers, Mark Spencer Yancey, a Dallas financial adviser, and Dwayne Stovall, who finished third in the 2014 GOP primary.

Fallon, 51, successfully challenged Craig Estes, a fellow Republican, for his state senate seat in 2018. He previously served in the Texas House of Representatives for six years. Fallon is not up for re-election until 2022.

A former U.S. Air Force Officer, Fallon completed the World Marathon Challenge in 2016, running seven marathons on seven continents in seven days. The money he raised went to pediatric cancer research. He was the most prolific North Texas legislator last session, filing 113 bills. One of the nine he passed into law as a primary author makes it a capital crime to murder someone under the age of 15.

In a statement to The News, Patrick said he remains behind Cornyn "100 percent."

"He is one of President Trump's strongest allies and has led the fight to confirm conservative judges to the federal bench and the Supreme Court," said Patrick, who leads the Texas Senate as its president. "He worked tirelessly following Hurricane Harvey and was successful in securing the resources Texas needed to rebuild. We need to re-elect John Cornyn to the U.S. Senate in 2020 and I will do all I can to help secure that victory."

Patrick endorsed Fallon over Estes in 2018.

The Democratic primary for the right to face the GOP candidate is already crowded. The field includes state Sen. Royce West of Dallas; MJ Hegar, the former Air Force helicopter pilot and businesswoman; Houston city council member Amanda Edwards; former U.S. Rep. Chris Bell of Houston; and Cristina Tzintzún Ramirez of Austin, who has spent a career as an organizer and activist for Texas workers and Hispanic voters.

Lauren McGaughy reported from Austin. Gromer Jeffers Jr. reported from Dallas.