Updated at 12:45 p.m. on Monday with Markle fund-raising tally.

WASHINGTON — First Beto O'Rourke wants to come after his guns, prompting Texas state Rep. Briscoe Cain to warn that he has an AR-15 "ready."

Now O'Rourke is going after Cain's seat in the Texas Legislature.

Late Saturday, O'Rourke urged his own supporters to pour money into the campaign of a Democrat hoping to oust Cain next year: Josh Markle, an Air Force veteran. His campaign biography says he works at a sign language interpreting agency and lives with his husband and their two dogs in Deer Park, the same Houston suburb that Cain lives in.

That marked an escalation in the feud that erupted during Thursday night's Democratic presidential debate, when O'Rourke, a former El Paso congressman, forcefully promoted a plan to enact mandatory buybacks of "weapons of war."

Briscoe Cain will not keep his seat in the TX House. And when I win TX House District 128, it will be because I got effective help from lots of people, particularly today from Beto. Beto’s fundraising email this evening for our campaign has blown us away. Thanks, @BetoORourke — Josh Markle (@MarkleTX128) September 15, 2019

"Hell, yes, we're going to take your AR-15, your AK-47. We're not going to allow it to be used against our fellow Americans anymore," he declared.

Staunch Second Amendment defenders view that as confiscation and an unconstitutional assault on their rights. Cain tweeted out an ominous warning, taunting O'Rourke by using his legal name: "My AR is ready for you Robert Francis."

Markle welcomed O'Rourke's help, which he would not have expected three days earlier.

"When I win TX House District 128, it will be because I got effective help from lots of people, particularly today from Beto," he tweeted. "Beto's fundraising email this evening for our campaign has blown us away."

As of Monday at noon, O'Rourke's appeal had driven more than $36,000 in donations to the Markle campaign, Markle said.

Texas Monthly, describing Cain as "uninformed and belligerent," put him at the top of its list of 10 worst state legislators. In June 2018, Cain was removed from the Texas Democrats' state convention in Fort Worth, where O'Rourke was the star speaker, after he and a handful of other Republicans handed out yard signs reading "This home is a gun free safe space" as a prank.

"It's amazing how many people took one and thanked us. They said they would put it in front of their house. I think it's funny," Cain told the Fort Worth Star-Telegram.

Speaking with reporters moments after Thursday night's debate at Texas Southern University in Houston, O'Rourke had clearly never heard of Cain. He speculated that if a buyback program of the sort he wants were enacted, he would expect Cain to obey the law.

By then, however, O'Rourke campaign aides had announced on social media that Cain's "death threat" would be reported to the FBI.

O'Rourke's demand for confiscation goes far beyond his stance during last year's Senate debate, when he called for a halt to U.S. production of assault-style weapons and a ban on imports, but assured voters that Americans could keep guns they already owned. After a gunman drove from a Dallas suburb to El Paso and killed 22 people at a Walmart, targeting Hispanics, O'Rourke said he reconsidered his views and decided that allowing 10 or 15 million such weapons to remain in civilian hands is not acceptable.

1 / 2State Rep. Briscoe Cain, Texas House of Representatives, Dist. 128 2 / 2Josh Markle, Democratic candidate for Texas House District 128.(Markle campaign courtesy photo)

Sen. Ted Cruz, who narrowly survived O'Rourke's challenge last year, pointed to the confiscation proposal as an example of the "radical" agenda on display at Thursday's debate in his hometown.

"They want open borders, they want to take away your health insurance, and they want to take away your guns," Cruz said Sunday on ABC's This Week, without singling out O'Rourke. "That is an agenda designed to resonate in the faculty lounges at an Ivy League college. If you're sipping sherry in a faculty lounge, you have got your party.

"But show me one steelworker, show me one truck driver, show me one person in America who actually works for a living who is interested in that radical agenda," he said.

Twitter removed Cain's original tweet, on grounds that it violated terms of service banning threats of violence, though by then it was in wide circulation.

Cain, 34, took office in 2017. His district east of Houston stretches from the Gulf city of La Porte north to Kingwood. He is part of the Texas Freedom Caucus, a group of far right conservatives in the state House.