Defense Secretary Ash Carter has refused to say whether NATO is relevant, saying that commenting on the matter is tied up in presidential politics.

Rep. Joe Courtney, D-Conn., asked Carter the question during a House Armed Services Committee hearing on Tuesday, noting that Brussels is the home of NATO and the alliance plays a major role in the United States’ strategy to protect Europe from Russia and fight the Islamic State in the Middle East. He cited comments from GOP front-runner Donald Trump, who raised the issue of the alliance’s relevance this week.