(NewsNation) — The heads of the U.S. Department of Homeland Security, National Counterterrorism Center and FBI will testify before Congress Tuesday about the biggest threats facing this country.

From terrorism abroad to the rise in U.S. domestic terrorism, cyber threats and election security, one of the main issues that will almost certainly come up is security at the southern border.

This hearing will be the first time Homeland Security Secretary Alejandro Mayorkas has spoken publicly since U.S. Customs and Border Patrol Commissioner Chris Magnus resigned on Nov. 12.

Magnus’ resignation followed reports that Mayorkas told him to either resign or be dismissed.

Under Magnus’ watch, the number of illegal crossings rose to the highest level ever recorded in a fiscal year. In the fiscal year that ended Sept. 30, migrants were stopped 2.38 million times, up 37% from the year before, according to newly released figures.

The annual total surpassed 2 million for the first time in August and is more than twice the highest level during Donald Trump’s presidency, in 2019.

Meanwhile, in Texas, Gov. Greg Abbott released a letter Monday reaffirming his commitment to securing the southern border, criticizing the Biden administration and asking Congress to “fulfill their responsibility to secure the border.”

To date, Abbott has bused more than 13,000 migrants to Washington, D.C., Chicago and New York.

Regarding election security, FBI Director Christopher Wray and National Counterterrorism Center Director Christine Abizaid will take part in a discussion regarding threats to election workers or elected officials.

In the weeks leading up to the midterms, these groups sent out a bulletin warning about the heightened risk of threats of violence at the polls or other election functions.

That bulletin came out the same day House Speaker Nancy Pelosi’s husband was attacked in their home in San Francisco.

The Department of Justice says election workers reported more than 1,000 threats or hostile interactions in the past few years.

On Thursday, Wray, Mayorkas and Abizaid will testify in a similar hearing in front of the Senate committee.