President Donald Trump on Thursday said he was not sure the United States should be spending anything on NATO, telling reporters the U.S. was protecting NATO members, but they were "not protecting us."

Trump has long demanded that other members of the transatlantic alliance spend more of the gross domestic product on defense after years of not meeting the NATO target of 2%.

Trump has said members of the military alliance should spend 5% of their gross domestic product on defense — a huge increase from the current 2% goal and a level that no NATO country, including the United States, currently achieves.