A top Border patrol official seemed to surprise a House Democrat on Tuesday by indicating that improving the "physical barrier" at the southern U.S. border would help control immigration flows and drug trafficking, and that the fencing already up at the border has made a noticeable improvement.

"We've seen great effect of the fencing, the wall that's there, on the southern border," Ronald Vitiello, acting chief of the U.S. Border Patrol, told a House Homeland Security subcommittee panel.

Vitiello offered that assessment in response to a thinly-veiled question about Republican candidate Donald Trump's pledge to build a border wall if he were elected president. "In this highly charged political environment, there's a lot of talk about building walls and building them higher than they were proposed previously," Rep. Brian Higgins, D-N.Y. "Is that a good expense of resources or are we much better off hiring more professional customs and border patrol?"

Vitiello assured him that "it matters if you have a physical barrier." He admitted that no such request has been made by any agents on the northern border, but said it "absolutely" has been made by agents on the southern border.

"So, in that regard, the physical barrier has improved the work of customs and border protection?" Higgins asked again.

"Absolutely, it has," Vitiello said.

The border patrol chief couldn't say how much of the southern border needs a wall, as he noted that part of the border is a sufficient "natural barrier" to illegal crossings.