For the first time since she was nominated by the Democratic Party for president, Kamala Harris is travelling to the southern border of the US.
Despite a sharp decline in the number of migrants entering our country in recent months, Donald Trump has been disparaging both President Biden's and her records on illegal immigration.
Trump asserts that "Kamala Harris has allowed 21 million illegals to pour in from all over the world."
Trump is held accountable by the Democrats, who claim he tried to obstruct the passage of a bill that would have increased border security.
So, what information do we have regarding those who cross it illegally?
How many migrants have crossed the US southern border?
Officials at the US border keep track of "encounters" with migrants, including those who try to enter the country illegally and those who try to enter lawfully but are denied entry.
Under the Biden administration, these interactions have reached all-time highs, but not to the extent that Trump asserts.
Over 10 million interactions have occurred since Joe Biden took office in January 2021; over 8 million of those encounters occurred across the southwest land border with Mexico.
On this border, there were 2.4 million interactions during the Trump presidency.
As a result of the pandemic, encounters decreased at the beginning of 2020 as arrivals slowed.
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.
In response, Biden issued an executive order in June 2024 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.
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Source: BBC Verify