Over the years, Rodrigo Duterte's regular rants about the U.S. appeared to amount to little more than bluster. This week the Philippine leader finally moved to dismantle an alliance that has endured since World War II.

Duterte's administration on Tuesday notified the U.S. it would terminate the Visiting Forces Agreement, which has governed military cooperation between the two countries since 1998. It is key to implementing a mutual defense treaty signed in 1951, shortly after the Philippines achieved independence from the U.S.

The move, spurred by the Trump administration's refusal to give one of Duterte's political allies a visa, triggered a six-month notification period before it expires. Now the question is whether the Philippine leader will go even further in shunning the country's main security partner, or if he is simply using this as a negotiating tactic to get a better deal from Trump.