In the midst of the debate about Donald Trump's proposed border wall with Mexico, his Republican presidential candidate rival Scott Walker is arguing that building a fence along the U.S.-Canadian border is worth considering.

"Some people have asked us about that in New Hampshire," the Wisconsin governor told NBC's Chuck Todd in a "Meet the Press" interview that aired Sunday. "They have raised some very legitimate concerns, including some law enforcement folks that brought that up to me at one of our town hall meetings about a week and a half ago. So that's a legitimate issue for us to look at."

At 5,525 miles, the boundary between the United States and Canada is the longest international border in the world -- though it is anything but heavily controlled, the Associated Press pointed out.

"If we're spending millions of dollars on TSA at our airports, if we're spending all sorts of money on port security, it only makes sense to me that, if part of what we're doing is protect ourselves, and set aside immigration for a minute, but protect ourselves from risk out there, I think we should make sure we have a secure border," Walker argued.

But Vermont Sen. Patrick Leahy, whose state also borders Canada, slammed the governor on Monday for what the Democrat said was "one of the craziest" ideas he had heard so far this election season.

"As someone who was born and raised not too far from the Canadian Border, I could not believe Governor Walker's statement," Leahy wrote in his retort. "Governor Walker simply must be unaware of the economic prosperity that commerce across the northern border brings to the United States. Those of us who represent states that share a border with Canada know better."

Canadian officials, for their part, also criticized the Republican, the CBC noted. "Of course, we would vigorously oppose any thickening of the border," the country's defense minister Jason Kenney told a news conference in the capital of Ottawa.