Beto O'Rourke made a bold gun control vow Thursday night at the 2020 Democratic debate, saying: 'Hell, yes, we are going to take your AR-15s.'

The former Texas congressman was applauded by the Democratic audience but risked handing Republicans red meat for attack advertisements if he makes it to the head-to-head race with Donald Trump.

O'Rourke has made outspoken attacks on the Republicans and Donald Trump in particular over guns the centerpiece of his campaign in the wake of mass shootings in Texas, most recently at Walmart in El Paso.

But making the declaration on the debate stage reaches a wider audience - and could be used against him. It gained an instant response from an ultra-conservative Texas lawmaker, who tweeted: 'My AR is ready for you.'

Since Briscoe Cain posted the message, Twitter removed it for violating the social media platform's policies.

During the debate O'Rourke got heated talking about the need to eliminate assault weapons after the mass shootings in El Paso and Odessa in a passionate speech that had the audience cheering him on.

'If it's a weapon that was designed to kill people on a battlefield. If the high impact, high velocity round, when it hits your body, shreds everything inside of your body because it was designed to do that so you would bleed to death on a battlefield and not be able to get up and kill one of our soldiers.

O'Rourke got heated talking about the need to eliminate assault weapons after the mass shootings in El Paso and Odessa in a passionate speech that had the audience cheering him on

Instant reaction: A conservative Texas state lawmaker's response to O'Rourke gave the 2020 candidate's policy more time in the spotlight

'When we see that being used against children and in Odessa, I met the mother of a 15-year-old girl who was shot by an AR-15 and that mother watched her bleed to death over the course of an hour because so many other people were shot by that AR-15 in Odessa, there weren't enough ambulances to get to them in time.

'Hell, yes, we're going to take your AR-15, your AK-47. We're not going to allow it to be used against a fellow American anymore, he said as the audience broke into long applause.'

Shortly after his intervention, his campaign tweeted a clip of it and a link to his fundraising website, suggesting he had practiced the line in advance.

Outspoken Texas Republican state lawmaker, Briscoe Cain, took up the challenge, tweeting 'My AR is ready for you Robert Francis'

Then an outspoken Texas Republican state lawmaker, Briscoe Cain, took up the challenge, tweeting 'My AR is ready for you Robert Francis.'

O'Rourke's twitter account responded: 'This is a death threat, Representative. Clearly, you shouldn't own an AR-15—and neither should anyone else.'

Cain is a controversial figure who also mocked the death of Stephen Hawking, the physicist and prominent atheist by tweeting: 'Stephen Hawking now knows the truth about how the universe was actually made. My condolences to his family.'

There had been bickering between the candidates when they were asked about their response to the recent spat of mass shootings that have taken place in the country.

Joe Biden was asked why voters should trust him to lead on the issue when President Obama asked him to work on background checks after the 2012 Sandy Hook Elementary School shootings and a measure to expand the checks died on the Senate floor.

'Because I've got it done before,' the former vice president said. 'I'm the only one up here that's ever beat the NRA. Only one to beat the NRA nationally. I brought the Brady bill into focus and became law. And so, that's number one. Number two, after Sandy Hook, a number of things happened. It went from a cause to a movement,' he said.

The Brady Bill that Biden referred to was a 1993 law signed by President Bill Clinton was Biden was a senator from Delaware. It mandated federal background checks on firearm purchasers in the United States, and imposed a five-day waiting period on purchases, until the NCIC system was implemented in 1998.

'So, the point is, things have changed,' Biden said, 'and changed a lot.'

He then went on to praise O'Rouke for his response to the August shooting a Wal-Mart in his home town of El Paso where a mass shooter killed 22 people and injured 24 others.

'By the way, the way Beto -- forgive me for saying Beto, congressman,' Biden said to O'Rourke.

Shortly after his intervention, his campaign tweeted a clip of it and a link to his fundraising website, suggesting he had practiced the line in advance.

'That's okay. Beto's good,' O'Rourke responded.

'The way he handled what happened in his hometown is meaningful. To look into the eyes of those people, to see those kids, to understand those parents, you understand the heartache,' Biden said.

But Biden was also asked why he said assault weapons cannot be outlawed for purchase by executive order.

'Some things you can. Many things you can't,' Biden said.

But Harris attacked him, using Barack Obama's 2008 campaign slogan.

'Well, I mean, I would just say, hey, Joe, instead of saying, no, we can't, let's say yes, we can,' the California senator said.

'And yes, we can,' she added. 'It is overlooking the fact that every day in America, our babies are going to school to have drills.

'Elementary, middle and high school students, where they are learning about how they have to hide in a closet or crouch in a corner if there is a mass shooter roaming the hallways of their school.

'I was talking about this at one of my town halls and this child was 8 years old, probably, came up to me. It was like it was a secret between the two of us, he tugged on my jacket and he said, I had to have one of those drills. It is traumatizing our children.'

She then praised O'Rourke for his work in El Paso and got in an attack at President Trump.

'Beto, God love you for standing to courageously in the midst of that tragedy. People asked me in El Paso, they said, you know, because I have a long-standing record on this issue.

'They said, do you think Trump is responsible for what happened? And I said, well, look, obviously he didn't pull the trigger, but he certainly been tweeting out the ammunition,' Harris said.

Booker said he was happy to see the ideas but sorry it took so long.

'I'm happy that people like Beto O'Rourke are showing such courage now and coming forward and also now supporting licensing.

'But this is - what I'm sorry about, I'm sorry that it had to take issues coming to my neighborhood or personally affecting Beto to make us demand change,' the senator from New Jersey said.

'I will lead change on this issue because I have seen what the carnage creates in communities like mine, because we forget, national shootings, these mass shootings are tragedies, but the majority of the homicide victims come from neighborhoods like mine.

'Nobody has ascended to the White House that will bring more personal passion on this issue. I will fight this and bring a fight to the NRA and the corporate gun lobby like they have never seen before,' Booker vowed.