WASHINGTON — Wisconsin Gov. Scott Walker is putting a new twist on the topic of securing the border, a staple among the Republican candidates running for president, by pointing north.

Walker said in an interview that aired Sunday that building a wall along the country’s northern border with Canada is a legitimate issue that merits further review.

Republican candidates for president have often taken a get-tough approach on deterring illegal immigration, but they usually focus on the border with Mexico. Walker was asked Sunday morning on NBC’s “Meet the Press” whether he wanted to build a wall on the northern border, too. Walker said some people in New Hampshire have asked the campaign about the topic.

“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. So that is a legitimate issue for us to look at,” Walker said.

The U.S.-Canada boundary is the longest international border in the world at 5,525 miles (8.891 kilometers) long.

Billionaire Donald Trump is riding the issue of illegal immigration to the top of the Republican presidential primary polls. He has said he would make Mexico pay for completing a permanent wall along the border. He also says he would also end automatic citizenship for those born in the United States, a right guaranteed by the 14th Amendment to the Constitution that was originally added to grant citizenship to freed slaves and their descendants after the Civil War. His positions appear to have pushed rivals to also take strong stands on immigration.

Walker, at one point, echoed Trump’s call for ending birthright citizenship, but later said he is against any such repeal.

As Trump has gained support, Walker has slipped in the polls to the middle of the pack of 17 Republican candidates. Several months ago, he led the polls in Iowa whose caucuses in early February will kick off the state-by-state nominating contests, but trails both Trump and retired neurosurgeon Ben Carson in the latest poll.