Get all the latest news on coronavirus and more delivered daily to your inbox. Sign up here.

The election of Joe Biden as president will erase all the gains the Trump administration has made on the southern border amid a decline in illegal crossings, warned former Immigration and Customs Enforcement Acting Director Thomas Homan.

Homan, pitching his new book, "Defend the Border and Save Lives: Solving Our Most Important Humanitarian and Security Crisis," predicted during a virtual interview with the Center for Immigration Studies that a surge in unlawful crossings will begin on "Day One" of a Biden presidency.

“All the success President Trump has made, 80 percent decline on the southern border, goes away, Day One, if he doesn’t retain the presidency,” he told CIS Executive Director Mark Krikorian during the interview Tuesday. “We lose the border.

"Joe Biden has always went on record saying 'we won't deport illegal aliens unless they're convicted of a serious felony,'" Homan added. "What kind of message does that send to the rest of the world?"

Homan, who served as acting director of ICE before leaving in 2018, is a big supporter of President Trump's hardline immigration policies. During the interview, he defended Trump's much-promised border wall, ICE detention centers and said Democrats would use immigration to attack the president.

“They want to make immigration an issue for 2020. They want to try to show that this president has failed on his No. 1 campaign promise and has been unsuccessful,” he said, adding that Trump received no help from Congress. "He's been very successful doing it all by himself."

He cited the "remain in Mexico" policy that was temporarily blocked by a federal appeals court. The policy allows the government to return immigrants seeking asylum to Mexico to wait out their cases in the United States.

CLICK HERE TO GET THE FOX NEWS APP

The Supreme Court in March upheld the policy.

“The day they said we’re going to stop the remain in Mexico program, hundreds, hundreds of illegal aliens in Mexico were lining up to come across the border,” he said. “It was within hours of that decision that we were looking at another surge. It’s proven itself."