A hearing in the Senate on migrant children and America’s illegal immigration loopholes on Tuesday highlighted seven statistics that explain why the system does not function properly.

The numbers are not new.

But they demonstrate the scope of the problem — and explain the impact of several obstacles that frustrate swift and efficient enforcement of immigration laws in the U.S.

These seven key points below are worth considering.

1.) The numbers of unaccompanied minors who cross the southwest border have gone from a trickle to a flood. Authorities apprehended fewer than 4,000 young people in fiscal year 2009 — but a stunning 68,541 in fiscal year 2014.

With one month left to go in this current fiscal year, the total right now is 53,183.

2.) Apprehensions of adults traveling with children — termed “family units” by the Department of Homeland Security — also have skyrocketed.

After that figure totaled 68,445 in fiscal year 2014, Barack Obama’s administration started detaining families pending the outcome of immigration cases. Apprehensions of families dropped 42 percent the following year. But then a federal judge in July 2015 reinterpreted a court settlement that had barred long-term detention of unaccompanied minors, which shut down family detention.

Border crossings by adults and children began rising again. They’ve now exceeded 124,000 for the first 11 months of the current fiscal year.

3.) Asylum claims by illegal immigrants from El Salvador, Honduras and Guatemala continue to spike, with little change in that region’s murder rates, which supposedly are what drive people here.

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In fiscal year 2009, a total of 5,275 people made “credible fear” claims, triggering asylum proceedings. By fiscal year 2016, the number was 66,899 from those three Central American countries alone.

4.) Illegal immigrants who are detained are far more likely to be deported than illegal immigrants who are allowed to wait for immigration hearings inside the United States.

A June 2017 study by the Institute for Defense Analysis — commissioned in 2014 by the Obama administration — found that 77 percent of detained illegal immigrants wound up getting deported. The deportation rate of those who were not detained, though, was only 7 percent.

5.) One reason that deportations are low for illegal immigrants who aren’t detained is that they often skip out on immigration court hearings. The absconder rate for family units over the past four fiscal years has ranged from 23 percent to 31 percent.

6.) A program called Alternatives to Detention (ATD), which seeks to monitor those illegal immigrants who are awaiting court hearings, met its goal for deportations. But that goal was rather modest; of 40,864 people who spent at least one day in the ATD program in fiscal year 2013, only 2,901 — 7 percent — ended up getting deported that year.

7.) Nearly 80 percent of the sponsors with whom unaccompanied minors are placed are themselves living illegally in the United States.

Related: Four Immigration Facts Mainstream Media Won’t Tell You

The data emerging from the Senate Homeland Security and Governmental Affairs Committee strongly demonstrate that the “pull” factors play a much bigger role in illegal immigration than the “push” factors, said its chairman, Sen. Ron Johnson (R-Wis.), at the hearing.

He showed a chart illustrating that asylum claims are zooming up — while the line depicting homicides is mostly straight.

“Even though murders have stayed relatively steady in terms of murder rates — you know, very high, yes, unacceptably high in Central America — asylum claims have shot up in the last couple of years,” he said. “So there’s some disconnect here in terms of cause and effect.”

“That’s when those individuals will abscond. If they have a bracelet, as we’ve seen with many individuals now — especially with family units — they will cut those bracelets.”

Committee Democrats did their best to keep the focus on the now-ended policy of charging parents with illegal border crossing and putting them in jail — while placing their children in facilities run by the Department of Health and Human Services, and later with sponsors in the United States.

“We cannot lose sight that they are families … No one should be separating children from their parents,” said ranking Democratic Sen. Claire McCaskill of Missouri.

Joseph Edlow, acting deputy assistant attorney general, testified that immigration courts prioritize cases where illegal immigrants are in detention. That adds to the backlog of nondetained illegal immigrants.

But Edlow said if the number of those detained increases, those cases also would take priority.

“We do not have a backlog now [among detention cases]. We would not have a backlog then,” he said.

Detention vs. monitoring. Matthew Albence, executive associate director of U.S. Immigration and Customs Enforcement (ICE), said his agents mostly are busy tracking down illegal immigrants who have committed other crimes. He does not have the resources, he said, to hunt run-of-the-mill illegal immigrants who abscond from court hearings.

The Government Accountability Office found that 99 percent of foreigners in the ATD in fiscal years 2011 through 2013 showed up for court hearings. But Albence said the high compliance rate applies to the initial court hearing; compliance with electronic monitoring drops dramatically if the immigrants lose their cases.

“That’s when those individuals will abscond,” he said. “If they have a bracelet, as we’ve seen with many individuals now — especially with family units — they will cut those bracelets.”

McCaskill demanded to know why ICE stops monitoring after immigration courts rule. Albence cited cost. He said illegal immigrants often flee after an unfavorable court ruling, during a 30-day appeal period.

“They will comply up to the point when the benefit of complying is no longer there,” he said.

Albence also said ICE saw similar disappointing results from a program specifically tailored for illegal immigrant families.

Related: Illegal Border Crossings Spiked 16.4 Percent in August

“Overall, the compliance rate was a little bit less than our normal program, at a much higher expense,” he said. “And ultimately [it] only resulted in 15 removals at a cost of $1.16 million per removal.”

The Trump administration, above all, would like Congress to pass a law repealing the 1997 court agreement — the so-called Flores settlement — that prevents long-term detention of children.

Edlow said the administration is working on regulations that might alleviate some of the problem. But Johnson expressed skepticism that it would be successful.

“The courts will intervene, and this rule-making will never be put in effect,” he said.

Edlow said the Justice Department stands ready to defend against any legal challenge. But he added, “Legislation would be preferable.”

Check out the questioning of witnesses at the hearing by Sen. James Lankford (R-Okla.).