WASHINGTON (AP) — President Joe Biden on Tuesday said Donald Trump's comments calling into question the U.S. commitment to defend its NATO allies from attack were "dangerous" and "un-American," seizing on the former president's comments that sowed fresh fears among U.S. partners about its dependability on the global stage.

Trump, the front-runner in the U.S. for the Republican Party's nomination this year, said Saturday that he once warned that he would allow Russia to do whatever it wants to NATO member nations that are "delinquent" in devoting 2% of their gross domestic product to defense. It was the latest instance in which the former president seemed to side with an authoritarian state over America's democratic allies.

Speaking from the White House as he encouraged the House to take up a Senate-passed aid bill to fund Ukraine's efforts to hold off a two-year Russian invasion, Biden said Trump's comments about the mutual defense pact were "dangerous and shocking."

"The whole world heard it and the worst thing is he means it," Biden added.

Biden said that "when America gives its word, it means something," and called Trump's comments sowing doubt about its commitments "un-American."

Biden said of Trump: "He doesn't understand that the sacred commitment that we've given works for us as well."

NATO's Article 5 mutual defense clause states that an armed attack against one or more of its members shall be considered an attack against all members. But Trump has often depicted NATO allies as leeches on the U.S. military and openly questioned the value of the military alliance that has defined American foreign policy for more than 70 years.

Since the full scale Russian invasion of Ukraine in 2022, Biden has ushered Finland into the alliance and is clearing the way for Sweden to do the same. While Ukraine is not a member of NATO, the alliance has served as a key contributor of the U.S.-organized effort to support Kyiv's military defenses in the nearly two year old conflict.

NATO allies agreed in 2014, after Russia annexed Ukraine's Crimean Peninsula, to halt the spending cuts they had made after the Cold War and move toward spending 2% of their GDP on defense by 2024. The spending target is not a requirement for NATO members.

NATO's secretary-general, Jens Stoltenberg, said in a statement Sunday that "any suggestion that allies will not defend each other undermines all of our security, including that of the U.S., and puts American and European soldiers at increased risk." The defense minister in Poland, which has been under Russian control more often than not since the end of the 18th century, said "no election campaign is an excuse for playing with the security of the alliance."

"President Trump got our allies to increase their NATO spending by demanding they pay up, but Joe Biden went back to letting them take advantage of the American taxpayer," said Jason Miller, a Trump senior adviser, in response to Biden's comments. "When you don't pay your defense spending you can't be surprised that you get more war."

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AP writers Seung Min Kim and Jill Colvin contributed.