President Obama was taken aback by a question about Donald Trump.

“Oh no,” he replied when ABC News reporter Mary Bruce asked him about Trump’s foreign policy. Obama had been discussing corporate tax loopholes.

In his answer, the president specifically focused on Trump’s proposal to block billions of dollars in remittances sent by immigrants to Mexico unless the country helped pay for a wall securing the Southern border.

“The implications with respect to ending remittances, many of which are from illegal immigrants and have individuals who are sending money back to their families, are enormous,” Obama said, calling the proposal “impractical.”

“The notion that we are going to track every Western Union, you know, bit of money that’s sent to Mexico, you know, good luck with that,” he shot back.

Obama warned that if the Mexican economy collapsed as a result of a payment blockade, more immigrants would likely flood into the United States.

“This is just one more example of something that is not thought through and is primarily put forward for political consumption,” Obama said, referring to Trump. He warned that serious problems faced the world who looked to the United States to successfully tackle them.

“They don’t expect half-baked notions coming out of the White House,” he said. “We can’t afford that. All right?”