The argument between President Trump and his Ukrainian counterpart caused serious damage to an alliance at the heart of the post-World War II order.

Donald Trump said on Wednesday that Ukraine should "forget" about joining NATO as the U.S. president prepares to welcome Volodymyr Zelenskyy to the White House this Friday.

Volodymyr Zelensky said he is "exchangeable" for Ukrainian membership to NATO while speaking to reporters in the UK.

Former NATO Supreme Allied Commander Wesley Clark said, “It's [hard] to look at Russia through Russian eyes. Most of us look at Russia, we say, ‘The economy’s in trouble, forces aren't going very far very fast,