Former President Trump's incendiary comments about NATO this weekend represent the most belligerent public posture he's taken against the Western alliance in his eight years as a politician.

Why it matters: In Europe, where the war in Ukraine is approaching its second anniversary, Trump's remarks supercharged the existing angst among NATO leaders who fear his potential return to the White House.

Back home, the comments had two major — and familiar — impacts:

1. Hijacking a bad news cycle for his likely election opponent, President Biden.
2. Forcing Republican allies to insist Trump didn't mean what he said.

Catch up quick: At a rally in South Carolina on Saturday, Trump claimed he told the president of an unidentified NATO member that he would "encourage" Russia "to do whatever the hell they want" to that NATO nation if it were behind on its defense obligations.

• The fallout was sharp and swift: Biden called the comments "appalling and dangerous," while NATO Secretary General Jens Stoltenberg warned that Trump's threats put U.S. and European soldiers "at increased risk."
• Article V of the NATO treaty — described as the "cornerstone" of the post-World War II alliance formed to protect Europe from the former Soviet Union — requires members to treat an attack on one ally as an attack on all of them. It has been invoked just once, after 9/11.
• Trump has long railed against NATO countries that do not spend 2% of their GDP on their military, though he frequently mischaracterizes the suggested target as part of a central fund that members pay into.

Zoom in: More telling than Trump's inflammatory rhetoric on NATO, which came as little surprise, has been the reaction from Republican hawks who criticized him in the past for far less provocative statements.

• Sens. Lindsey Graham (R-S.C.) and Marco Rubio (R-Fla.), who helped lead the charge on a bill that blocks the president from withdrawing from NATO without Senate approval, both defended his remarks this weekend.
• "NATO countries that don't spend enough on defense, like Germany, are already encouraging Russian aggression and President Trump is simply ringing the warning bell," Sen. Tom Cotton (R-Ark.), a top defense hawk, told the New York Times.
• Sen. Thom Tillis (R-N.C.), a co-chair of the Senate NATO Observer Group, said he doesn't think it's something Trump "honestly believes" — reprising the familiar Republican adage to take Trump "seriously, but not literally."

Between the lines: Trump privately discussed pulling out of NATO several times during his presidency, and former national security adviser John Bolton has warned that a U.S. withdrawal would "almost certainly happen" in a second Trump term.

The bottom line: Trump's campaign website features just one vague but ominous reference to his plans for the alliance: "[W]e have to finish the process we began under my administration of fundamentally re-evaluating NATO's purpose and NATO's mission."