() President Trump’s threats to abandon NATO members that don’t spend enough money on defense betray his ignorance about how the alliance works, former U.S. ambassador John Bolton said Thursday.

Trump this week renewed his criticisms of European allies, saying the U.S. may not help defend NATO members that fail to meet their budgetary commitment. Countries in the North Atlantic Treaty Organization are expected to set aside at least 2% of their gross domestic product, or GDP, for military purposes, but Trump has suggested that amount should rise to 5%.

“It’s an open invitation to the Russians,” the hawkish Bolton, who served as a national security adviser to Trump in his first term before they fell out, told ‘s “On Balance.”

Bolton said some NATO members meet their financial commitments while others do not. But he notes the U.S. would be foolish to ignore, say, an invasion of Iceland, which doesn’t have an army.

“Iceland, it seems to me, is Example A in Trump’s litany of who he’s not going to defend,” Bolton said. “So, he’s OK if the Russians and the Chinese invade and turn it into a big military base for them? What does Iceland bring to NATO, if it doesn’t have an army? It brings geography to NATO.”

Bolton has been a vocal critic of the president’s attempts to end the war in Ukraine, which has included friendly overtures to Russia. Last week, Trump and Vice President JD Vance clashed with Ukrainian President Volodymyr Zelenskyy in the Oval Office over a potential path to peace.

“Trump’s view of the world is simple minded, and the more he says what he says about Ukraine, the more delighted they are in Moscow,” Bolton said. “And the reasons the Russians haven’t come to the peace table yet is Trump is giving them, day after day, more than they thought to ask for.”

The United States, Canada and many European countries formed NATO in 1949 to halt aggression by the former Soviet Union. Ukraine has sought to join, but Trump has said that is not realistic if any peace deal is to be reached with Russia.