In news from the campaign trail, this weekend marks the South Carolina primary for Republicans and the Nevada caucus for Democrats. On Thursday, Pope Francis criticized Republican front-runner Donald Trump, suggesting the real estate mogul’s plan to build a wall on the U.S.-Mexico border means he is “not Christian.” Pope Francis spoke aboard his plane.

Pope Francis: “A person who thinks only about building walls, wherever they may be, and not building bridges, is not a Christian.”

Trump fired back at the pope, saying his comments were “disgraceful” and “unbelievable.” During the same news conference, the pope commented on the use of birth control in areas where Zika virus has led to public health emergencies. Scientists say the Zika virus may be linked to microcephaly, which causes infants to be born with unusually small heads. The pope appeared to make an exception for the use of birth control in such cases, saying, “Avoiding pregnancy is not an absolute evil.”