Before President Trump stepped up to a Rose Garden lectern on Friday to announce that he was declaring a national emergency, several women stepped out of the White House and took seats in the audience. They carried with them photographs of children or other loved ones who had been killed at the hands of people who were in the country illegally, either in intentional acts or accidents.

Trump referred to this group of mothers as the “angel moms” several times during his remarks and while fending off reporters’ questions about his declaration, meant to provide funding to build a wall on the border with Mexico.

“We have some of the greatest people I know. They’ve been with me from the beginning of my campaign — almost from the first week — the angel moms,” Trump said. He asked one mother to stand up and show a photo of her daughter. “I have such respect for these people, angel moms, angel dads, angel families,” he said. “I have great respect for these people. These are great people. These are great people. They’re fighting for their children that have been killed by people that were illegally in this country.”

When CNN’s Jim Acosta asked Trump whether the declaration of a national emergency wasn’t simply a concoction meant to get around Congress having rejected funding for the wall, Trump again cited the grief of those mothers.

“Ask the angel moms: What do you think? Do you think I’m creating something? Ask these incredible women who lost their daughters and their sons, okay?” Trump replied. “Because your question is a very political question, because you have an agenda. You’re CNN. You’re fake news — you have an agenda.”

That invocation is important. Trump often links illegal immigration to crime in broad terms (Mexico is “sending rapists,” for instance), bolstered with anecdotal examples of crimes committed by undocumented immigrants. Shortly before the midterm elections, Trump tweeted a video showing a grinning immigrant convicted of murder and juxtaposing that with scenes of a migrant caravan headed to the border. Trump’s reply to Acosta was, in short, that the wall is needed because an American died at the hands of an immigrant.

How many Americans are killed by undocumented immigrants isn’t clear. Trump has in the past cited a figure of 63,000, which is wildly exaggerated and stems from sloppy rhetoric offered by Rep. Steve King (R-Iowa) a decade ago. PolitiFact tried to learn how many murders might have been committed by undocumented immigrants and determined that the annual number was in the hundreds, not thousands. If the figure is 600 — at the upper end of PolitiFact’s estimate — that would make up about 3 percent of the murders tallied by the FBI in 2017.

Is declaring a national emergency and spending billions of dollars on the construction of a wall worth preventing 600 killings a year? Trump embraces parents who’ve lost children through accidents (such as car crashes) as well, so the number of people killed by undocumented immigrants is certainly higher than 600.

What isn’t clear is how much illegal immigration would be affected by more wall construction. Many migrants are smuggled through border checkpoints. Most illegal immigration in recent years has resulted when people who arrive on legal visas fail to leave when instructed. The wall wouldn’t affect that.

Trump also claims that building the wall will help address the nation’s opioid crisis, which in 2017 resulted in 70,000 deaths. That claim, though, is strongly disputed by information from Trump’s own administration. Most drugs that enter the country come through ports of entry, as well. It’s not clear that building more wall would significantly affect that flow.

The opioid crisis raises another question, too: Why isn’t that a national emergency? In 2009, President Barack Obama declared a national emergency to address a swine flu outbreak. Eight years later, Trump declared a public health emergency focused on opioids. If zero tolerance for preventable deaths is the watchword for the national-emergency declaration that Trump hopes will result in his wall, why doesn’t the opioid crisis warrant the same mobilization?

House Speaker Nancy Pelosi (D-Calif.) raised another possibility Thursday, the first anniversary of the mass shooting at a high school in Parkland, Fla.

"You want to talk about an national emergency? Let’s talk about today, the first anniversary of another manifestation of the epidemic of gun violence in America,” Pelosi said. “That’s a national emergency. . . . A Democratic president could do that.”

It’s a fair point, using Trump’s own standard: If he can declare an emergency to build a wall to try to keep immigrants out of the country and therefore prevent hundreds of deaths, why would he not call an emergency to take action to prevent the 40,000 gun deaths that occurred in 2017? Why not declare a national emergency to address the nation’s spike in suicides, with 45,000 in 2016, many of them with guns? (Suicides accounted for about 60 percent of the gun deaths in 2017.)

The answer lies in part with Trump’s proposed solution. It gets blurry when considering which came first — his desire to build a wall or his rhetoric about the need for one. But Trump has often cast the wall in almost messianic terms, a broad solution to crime and drugs across the United States, despite objective evidence that it would not be likely to solve the problem. (In a speech last month, Trump claimed without any evidence that some people said building a wall would cut the crime rate and drug problem in half.)

When asked by Acosta, Trump was left with little more of an argument than to point to the grieving families he had invited to attend his announcement. Their pain is moving, and no one would willingly trade places with them. No one would want other families to suffer the same fate. This is also true, of course, of those who’ve lost family members from gun violence, suicide or drug abuse.

But only one of those problems was the primary component of Trump’s campaign for president.