Republican Candidates Agree on Guns: 'We Stop Bad Guys by Using Our Guns' "We stop bad guys by using our guns," Ted Cruz said.

 -- The candidates in the crowded Republican field haven't been shy about taking potshots at one another, but today as they swarmed Iowa they showed unity over one issue -- guns.

Three days after 14 people were killed when a man and woman opened fire at the Inland Regional Center in San Bernardino, California -- the second mass shooting in less than a week -- the GOP candidates seemed to agree.

"We don't stop the bad guys by taking away our guns," Ted Cruz said. "We stop the bad guys by using our guns."

"If you are going to kill 15 people, do you think a control law is going to stop you?" said Rand Paul.

"A gun free zone is like meat to these animals," Donald Trump said, referring to bad guys.

The shooting, coming so soon after a gunman opened fire at a Planned Parenthood clinic in Colorado Springs, Colorado, killing three people, has heated up calls from Democrats for stricter gun control.

The issue also inspired the New York Times to run an editorial on its front page for the first time since 1920, saying the fact that civilians can purchase assault-type weapons "a moral outrage and a national disgrace."

Cruz repeated his lines from Friday that in the wake of the San Bernardino massacre and the attacks in Paris last month, the focus should be on radical Islamic terrorism and not on gun control.

Cruz showed that focus in a new TV ad airing in Iowa, in which he says, "Every Islamic extremist will know, if you wage jihad against us, you're signing your death warrant."

Along with the call to arms against terrorists, came calls from Cruz, Trump and Ben Carson for tighter restrictions on immigration.

Because alleged San Bernardino shooter Tafsheen Malik entered the United States last year on a K-1 visa -- the so-called "fiancee" visa -- Trump told ABC News today that he would consider shutting the program down.

"If people come in and the blow up people and they shoot people and they kill people, I don't rule out anything," he said. "We're going to have to start looking at people very closely because we cannot allow this to happen in our country."

Last year, 35,000 foreign fiances received K-1 visas and were admitted to the U.S. for marriage, according to the State Department. All underwent background checks and face-to-face interviews in a process that must be initiated by a U.S. citizen and takes months.

But Carson said the fact that Malik was able to pass through that system without being flagged indicates the process is flawed.

"That vetting resulted in missing someone who could carry out such a horrendous crime, that should be the end of the argument right there," he said.

Carson said it was also reason to end acceptance of Syrian refugees.

Democratic candidate Hillary Clinton said she was also concerned, telling Iowans something should be done to strengthen the vetting of visa applicants.

"Visas are a problem and we have to look at that and see what we need to do to tighten up requirements and do better," she said.