Despite words of praise for NATO at their joint news conference, Trump has repeatedly questioned NATO’s purpose and efficacy, calling it “obsolete,” while charging that the United States is saddled with paying an unfair share as a member. It was one of Mr. Trump’s most consistent messages in the months preceding his election. But if his views are strongly held, they’re relatively newly formed. The only mention of NATO on his Twitter feed before he hit the campaign trail was a single 2012 tweet lamenting that Israel, not a NATO member, was excluded from a NATO gathering in Chicago.