In an interview with CNN’s Jake Tapper Sunday morning, Acting Homeland Security Secretary Kevin McAleenan wasn’t able to articulate how or when the White House will end its tariffs on Mexican goods.

McAleenan appeared on cable news to defend President Donald Trump’s decision to impose new tariffs on Mexico as a means to address migration to the United States. The longer apprehension rates along the U.S.-Mexico border continue to rise, the higher the tariffs.

As the White House announced last week, a 5% tariff is set to go into effect on June 10 if Mexico does not step up immigration enforcement measures. The tariffs would gradually increase — an additional 5% on the first day of each month for four months — to a maximum of 25% by October, unless “the illegal immigration problem is remedied.”

Tapper asked McAleenan at what point would the administration consider lifting the tariffs, but McAleenan had no concrete response.

“I guess one of the questions I would have is assuming these tariffs go through, and right now it’s just a threat, what specific benchmark are you going to be looking at to see if Mexico is actually doing what you want them to do?” Tapper asked.

“I think what the president said, we need a vast reduction in the numbers crossing,” McAleenan replied.

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According to the Department of Homeland Security (DHS), there were roughly 100,000 apprehensions in April — so what would a “vast reduction” look like to the administration? McAleenan couldn’t answer that either.

Instead, McAleenan recommended the administration ask the Mexican government to enforce its own southern border with Guatemala, put an end to the organizations that help transport migrants across Mexico, and work with the United States on creating new asylum policies.

As ThinkProgress has previously reported, however, the Mexican government is already collaborating with the Trump administration on the immigration front, whether by arresting Central American migrants at the southern Mexico border or ordering bus operators to stop transporting migrants across the country.

Considering that the U.S. is one of Mexico’s biggest trade partners and even the preliminary 5% tariff could have devastating effects on the Mexican economy, this question is critical. U.S. imports of goods from Mexico totaled about $346.5 billion in 2018, according to the Office of the U.S. Trade Representative. Mexico, meanwhile, sends nearly 80% of its exports to the United States. Should tariffs reach the full 25% that Trump has threatened, American exporters of goods to Mexico would also be impacted, likely shoulder the cost of this new policy.

McAleenan also had no answers for how the U.S. would respond if Mexico’s economy took a downturn, causing more people to migrate.

“Bottom line for me is we need [Mexico] at the table looking at new strategies that we can aggressively move out on,” he said.