Republican presidential candidate Scott Walker thinks the U.S. should explore the prospect of building a wall along the longest international border in the world. The Wisconsin governor said on NBC's “Meet the Press” Sunday that he believes a wall between the U.S. and Canada is a "legitimate" issue that should be carefully considered.

Walker told "Meet the Press" host Chuck Todd that he got the idea from some voters he met in New Hampshire. “They 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,” Walker said.

The idea of securing America’s southern border with Mexico, either with a $22 billion wall or some other way, has long been a matter of debate among Republican candidates. Ever since it became clear in 2008 that a fence erected by the Department of Homeland Security was not getting the job done, candidates including former Arkansas Gov. Mike Huckabee and businessman Donald Trump have visited the border and vowed to do whatever was necessary to seal it.

The subject of America’s northern border with Canada -- the longest in the world, at more than 5,500 miles -- is discussed less frequently. According to the Pew Hispanic Center, just 5 percent of America’s illegal immigrants arrive from Canada and Europe, compared to 52 percent from Mexico.

And while some law enforcement officials have cited an influx of Canadian pharmaceuticals, particularly generic versions of painkillers such as OxyContin, as a concern, it pales in comparison to the volume of drugs that seeps through from Mexico every year.

Several months into the start of a very long race to select the Republican Party's 2016 presidential nominee, Walker has had trouble generating excitement or forward momentum. A poll recently released by Civis put Walker in seventh place among 17 Republican candidates, with support from just 5 percent of respondents. The same poll had Trump leading the Republican field, with support from 16 percent of respondents.