It isn't, which is why non-US NATO leaders have been scrambling recently to build new security arrangements.
> Why would Trump be so resistant to giving security guarantees and NATO membership to Ukraine if he didn't think holding to security guarantees like NATO was important?
Donald Trump unilaterally abandoning the NATO-wide commitment (announced in a joint communiqué of NATO Heads of State on February 25 immediately following North Atlantic Council consultations held under Article 4 of the Washington Treaty) on Ukraine [0] is major reason why NATO has become non-functional, with NATO allies, most especially those on NATO’s eastern flank who have been most adamant about Russia’s unchecked aggression against its neighbors posing an existential threat, distrusting American commitment and seeing the US as a threat rather than a reliable ally.
[0] “...We will continue to provide political and practical support to Ukraine as it continues to defend itself and call on others to do the same. We reaffirm our unwavering support for the independence, sovereignty and territorial integrity of Ukraine within its internationally recognised borders, including its territorial waters. This principled position will never change.”
It isn't, which is why non-US NATO leaders have been scrambling recently to build new security arrangements.
> Why would Trump be so resistant to giving security guarantees and NATO membership to Ukraine if he didn't think holding to security guarantees like NATO was important?
Donald Trump unilaterally abandoning the NATO-wide commitment (announced in a joint communiqué of NATO Heads of State on February 25 immediately following North Atlantic Council consultations held under Article 4 of the Washington Treaty) on Ukraine [0] is major reason why NATO has become non-functional, with NATO allies, most especially those on NATO’s eastern flank who have been most adamant about Russia’s unchecked aggression against its neighbors posing an existential threat, distrusting American commitment and seeing the US as a threat rather than a reliable ally.
[0] “...We will continue to provide political and practical support to Ukraine as it continues to defend itself and call on others to do the same. We reaffirm our unwavering support for the independence, sovereignty and territorial integrity of Ukraine within its internationally recognised borders, including its territorial waters. This principled position will never change.”