President Barack Obama's Department of Homeland Security secretary Jeh Johnson said "we are truly in a crisis" at the border during an appearance on MSNBC's Morning Joe on Thursday.

"When I was in office in Kirstjen Nielsen's job, at her desk, I'd get to work around 6:30 in the morning and there'd be my intelligence book sitting on my desk, the PDB, and also the apprehension numbers from the day before," Johnson said. "And I'd look at them every morning, it'd be the first thing I'd look at. And I probably got too close to the problem, and my staff will tell you if it was under 1,000 apprehensions the day before that was a relatively good number, and if it was above 1,000 it was a relatively bad number, and I was gonna be in a bad mood the whole day."

"On Tuesday, there were 4,000 apprehensions. I know that a thousand overwhelms the system. I cannot begin to imagine what 4,000 a day looks like, so we are truly in a crisis," Johnson continued.

A number of prominent Democrats have downplayed border security over the past year.

Sen. Kirsten Gillibrand (D., N.Y.), who is running for president, argued DHS should not oversee immigration because it is "not a security issue." Gillibrand and other Democrats have also called for abolishing Immigration and Customs Enforcement, with the New York senator calling it a "deportation force."

Rep. Jim McGovern (D., Mass.) and Rep. Alexandria Ocasio-Cortez (D., N.Y.) have echoed Gillibrand's sentiments.

Sen. Kamala Harris (D., Calif.), who is also running for president, has compared ICE to the Ku Klux Klan.