Joint Chiefs of Staff Chair Gen. Charles "CQ" Brown, Jr. told NBC News in an interview that the U.S.' credibility in its military alliances is "at stake" when asked to respond to former President Trump's recent comments on NATO.

Why it matters: Trump said at a South Carolina rally over the weekend he would not defend a NATO member against an attack by Russia if the country did not meet defensive spending levels obligated by the treat — and would "encourage" Moscow "to do whatever the hell they want" to such an ally.

What they're saying: "We have an alliance. We have a strong alliance," Brown told NBC News. "Matter of fact, this year is the 75th anniversary of NATO. "And I think we have a responsibility to uphold those alliances."

• Brown noted that his comments didn't just apply to NATO but also to the other defense obligations the U.S. has around the world, such as its agreements with Japan, South Korea, Australia and New Zealand.
• "U.S. credibility is at stake with each of our alliances and U.S. leadership is still needed, wanted, and watched," he added.

The big picture: Trump for years has publicly and privately criticized other NATO members for not meeting defense spending requirements, but his comments on Saturday marked a departure from his former complaints by vowing to not uphold Article 5, the alliance's collective defense clause.

• Not defending or providing military assistance to an attacked ally would violate a core tenet of the alliance: That all members will consider an attack against one an attack against all.
• Throughout his administration, Trump on multiple occasions said he wanted to withdraw the U.S. from the alliance, which would effectively amount to destroying it, the New York Times reports.
• The Senate passed legislation last year that would prevent a president from withdrawing the country from NATO without congressional approval, but there are several other ways Trump could undermine the treaty.
• Doing so would harm other U.S. alliances while emboldening Russia, China and other governments with expansionist desires.

The interview airs tonight on NBC Nightly News with Lester Holt at 6:30 pm ET.

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