Getty ImagesCracking down on illegal immigration has been Donald Trump’s signature issue – but now Democrats are trying to address an election weakness by also talking tough about securing the US border with Mexico.
The Republican presidential nominee has repeatedly criticised the government's record on the border, saying "Kamala Harris has allowed 21 million illegals to pour in from all over the world.”
Crossings did reach record levels under President Biden, but numbers have dropped significantly in recent months. Now Harris says she will make it even harder for migrants to seek asylum in the US.
Six out of 10 Americans rate immigration as “very important” in determining how they will vote, according to the Pew Research Center. Other polling suggests voters trust Trump to handle the issue more effectively than Harris.
So how have both administrations dealt with the influx of migrants and what do we know about the people crossing this border illegally?
How many migrants have crossed the US southern border?US border officials record "encounters" with migrants – these include people who attempted to cross illegally and people who tried to enter legally but were deemed inadmissible.
These encounters have risen to record highs under the Biden administration but not to the level Trump – who has not provided a source for his claim – maintains.
Since January 2021, when Joe Biden came to office, there have been more than 10 million encounters – about 8 million came over the southwest land border with Mexico.
Under the Trump administration, there were 2.4 million encounters on this border.
Encounters fell at the start of 2020 as arrivals slowed because of the pandemic.
The number of encounters is not a count of individuals who stay in the US as some migrants will be returned and the same person can be recorded trying to enter multiple times.
These figures don't include people who may have crossed the border undetected.
The US Department of Homeland Security has estimated there were 11 million illegal migrants living in the US as of January 2022.
It says about a fifth of them arrived in 2010 or later but the majority arrived before this time, some as early as the 1980s.
How have government policies affected border crossings?Both the Trump and Biden administrations used a Covid-19 public health measure to quickly return migrants at the border.
Between its start in March 2020 and its end in May 2023, migrants were expelled nearly three million times under this policy.
Despite this, encounters continued to increase, according to the Migration Policy Institute.
The factors driving this included a post-lockdown surge in crossings and political and economic instability in countries such as Venezuela.
Republicans say Biden’s “weak” policies on immigration also encouraged migrants to travel to the US – and some Democrats in border states criticised the administration for not acting quickly enough to address the crisis.
An attempt to pass a cross-party bill to tighten border security failed in May 2024, with Harris saying that Trump "tanked it".
Biden issued an executive order the following month to quickly deport migrants at the border.
This means migrants can be sent back without having their asylum claims processed, if the average number of weekly encounters exceeded a certain threshold.
A month after the order was introduced, encounters at the southern border fell by a fifth.
Efforts by the Mexican government have also brought crossings down, including setting up new checkpoints and increasing patrols.
In May, Mexican President Andrés Manuel López Obrador said that the number of migrants at the US southern border had halved from a peak of 12,000 a day to 6,000 a day.
