National emergency: Is there a crisis on the US-Mexico border?
President Donald Trump says he will declare a national emergency to fund a planned border wall with Mexico.
Announcing his plans at the White House, the president repeatedly used the term "invasion" to describe the situation on the US southern border.
His plan will bypass Congress and re-direct military funds to fund his long-promised barrier.
Critics say his government has created a "manufactured crisis".
They argue his assertions about the situation are untrue, and say there are far fewer people crossing the border than in previous decades.
So what's really happening?
How many people are crossing the border illegally?
It's impossible to say for certain but apprehensions made by US Customs and Border Protection (CBP) agents provide one measure.
CBP made a total of 396,579 apprehensions on the south-western border in fiscal year 2018, and 303,916 in 2017.
The number had fallen dramatically in President Trump's first year but rose again last year.
Looking at the wider picture, there has been a sharp fall in the number of people arrested in the last 18 years.
So, is there a current "crisis" of illegal immigration on the southern border?
"No," says Jacinta Ma, director of policy and advocacy for the National Immigration Forum, which advocates on behalf of immigrants.
"Even with the rise in apprehensions over the last year, it's way down from the early 2000s."
Do most illegal entries take place at the southern border?
Illegal border crossings are not limited to the southern border - in 2017, for example, there were also 3,027 illegal apprehensions along the Canadian border and 3,588 from the coastal border.
While cross-border migrants often make headlines, the largest number of illegal migrants settling in the US each year is those who stay in the country after their visas expire.
According to the most recent reports by the Department of Homeland Security (DHS) and the Center for Migration Studies, a non-partisan think-tank, the number who overstayed their visas has outnumbered those who crossed the border illegally every year since 2007.
In 2017, Canadians made up the largest group of these illegal migrants that entered by air or sea port of entry, followed by Mexicans (it should be noted that the majority of Canadians and Mexicans enter the US by land, and the DHS Overstay Report only provides air and sea overstay rates).
In 2016, there were a total of 739,478 overstays, compared to 563,204 illegal border crossings.
It's also important to note that, according to the Pew Research Center, overall the number of immigrants living in the US illegally has actually declined since 2007, in large part due to a dip in the number of people coming from Mexico. Apprehensions at the south-western border peaked in 2000, at 1.64 million.
In total, Pew estimates that in 2016, there were 10.7 million unauthorised immigrants living in the US.
How many people are attempting to cross legally?
Apprehension numbers released by the CBP include asylum seekers (a person who applies for refugee status at a US port of entry or from within the country).
In fiscal year 2018, 92,959 people were deemed to have made claims of credible fear" and asked for asylum at the border. That's a pretty big jump from fiscal year 2017, when 55,584 claims were made.
Kate Jastram, senior staff attorney for the Center for Gender and Refugee Studies at the University of California Hastings College of the Law, says that families fleeing violence in Central America began to make up a much larger part of border crossings beginning in 2014.
She says that has more to do with conditions in those countries than any immigration policy implemented by the Trump administration.
"Single men from Mexico were by and large not seeking asylum, they were looking for work," says Jastram. "[Now] we have families and children specifically seeking protection."
In November, a caravan of 7,000 migrants arrived at the US-Mexico border, many claiming to be fleeing violence in countries like Honduras, Guatemala and El Salvador. Mr Trump labelled the caravan an "invasion".
Overall, the rate of asylum denials is on the rise in the US, and has been for the past six years.
What has the Trump administration done to address all this?
Over the past two years, President Trump and his administration have tried a variety of deterrent measures affecting both illegal entrants and asylum seekers.
- asylum seekers caught crossing illegally must wait across the border in Mexico for adjudication
- border officials have decreased the number of asylum cases they process each day, a strategy called "metering"
- in June, then-Attorney General Jeff Sessions announced that claims of domestic and gang violence would no longer qualify as grounds for asylum in the US - this was defeated in court
- most controversially, in spring, thousands of migrant children were separated from their parents at the border as a part of a "zero tolerance policy" that prosecuted anyone found crossing illegally
Mr Trump has now said he will declare a "national emergency" in order to force through his border wall funding.
- Can Trump declare a national emergency to build a wall?
- Who decided to take away children at the US border?
Legal and constitutional scholars are divided on whether or not the president has the power to do such a thing, or if the laws exist to accomplish what he wants.
The president has said that he expects legal challenges to his plan.
What about terrorists?
It was an eye-catching claim from the White House press secretary.
"Last year alone there were nearly 4,000 known or suspected terrorists that CBP picked up that came across our southern border," Sarah Sanders told Fox and Friends.
That is not true. Even her colleague, Kellyanne Conway, later called it "an unfortunate misstatement".
So where did that figure come from?
A White House briefing report on immigration says 3,755 known or suspected terrorists were prevented from entering the US in the fiscal year 2017.
But that includes terror suspects who have been stopped at any US border, and the vast majority are stopped at airports.
"The debate is over a land border wall. To include airport statistics is irrelevant and misleading," says Todd Bensman from the Center for Immigration Studies, a think tank which favours lower immigration.
Bensman, a former counter-terrorism intelligence manager who worked at the Texas border, analysed data from a "reliable intelligence community source" and concluded that more than 100 migrants on terror watchlists were apprehended at the southern border between 2012-17.
Data from NBC News seems to support his assertion. It learnt that in the first half of 2018 six immigrants on the terror watchlist were stopped at the southern border
No-one who has crossed the US southern border illegally from 1975 to the end of 2017 has been responsible for a terror attack on US soil, according to David Bier and Alex Nowrasteh of the Cato Institute.
Seven so-called "special interest aliens" were convicted of planning an attack on US soil, during that time, says the libertarian think tank's report.
But that category includes any visitor from a country deemed by the US intelligence community as a risk. In the past it has been a list of 50 countries.
Reporting by Micah Luxen, Jessica Lussenhop and Rajini Vaidyanathan