America is losing its patience — that was the message Defense Secretary Jim Mattis communicated Wednesday at a meeting of defense ministers from NATO countries. Mattis warned, “America will meet its responsibilities, but if your nations do not want to see America moderate its commitment to the alliance, each of your capitals needs to show its support for our common defense.” Mattis statements echo those of Donald Trump when he warned during his campaign that NATO countries needed to pull their weight because doing otherwise is “very unfair to the United States.”

Currently only five of the 28 NATO countries pay the agreed upon 2% of each respective member nation’s GDP on defense. This isn’t a new problem either. Barack Obama also pushed for NATO members to increase their spending on defense (while cutting our own, we might add). What is new are the comments from Trump and Mattis that imply the U.S. might alter its commitment to NATO should those nations not meet their spending obligations.

Historically, NATO is the U.S.‘s most important and significant alliance. The U.S. benefits just as much from NATO as do the other member nations. It proved to be highly beneficial both during the Cold War and since 9/11 with the resulting war on terror. Mattis’s statements couldn’t come at better time given Russia’s steadily increasing aggression. News just this week of Moscow violating a treaty by moving intermediate range missiles testifies to this reality.

Mattis is seeking to once again assert U.S. leadership in NATO, which has been sorely lacking under the Obama administration. He has pulled out the proverbial stick in seeking to prod NATO members into meeting their agreed upon obligations. If those member nations continue to shirk responsibility, then there should be consequences. This is the tricky balance Trump is having to strike.