Hypersensitive to criticism of his deadly drug war, Philippine President Rodrigo Duterte has made a habit of questioning the future of his country’s longstanding alliance with the U.S.
While Obama administration officials have repeatedly stressed the strength of the relationship, here’s a look at what it would take for Duterte to follow through with his threat to "break up with America."

1. What official defense agreements are in place?

Three of them: the Mutual Defense Treaty signed in 1951, the Visiting Forces Agreement signed in 1998 and the Enhanced Defense Cooperation Agreement signed in 2014.
The Mutual Defense Treaty came into force after the U.S. granted the Philippines independence, and has been at the center of defense relations ever since. The eight-article pact -- one of seven collective U.S. defense treaties -- calls for each side to help build the ability to resist armed strikes, and “meet the common dangers in accordance with its constitutional processes" if either side is attacked.

The Visiting Forces Agreement is a longer, more detailed pact that spells out the legal details for U.S. military personnel operating in the Philippines. It covers everything from passport regulations to procedures for importing military equipment to criminal jurisdiction.

The most recent agreement is the Enhanced Defense Cooperation Agreement, which was reached between the Obama administration and President Benigno Aquino, Duterte’s predecessor. The pact allows for a greater U.S. presence at Philippine military bases and the construction of new facilities within those bases.

2. What are Duterte’s issues with the agreements?

Duterte has questioned whether the U.S. would defend the Philippines if China seizes disputed shoals and reefs in the South China Sea -- skepticism that has persisted in the Southeast Asian nation for decades. It’s unclear what would happen if the U.S. Congress fails to approve a military response, and whether contested territory is covered. A U.S. diplomatic cable from 1976, since declassified, states that treaty does not cover disputed areas such as the Spratly Islands.

3. Could Duterte end the agreements, and what’s the procedure?

He could, but it would take awhile. The Mutual Defense Treaty, ratified by the Senate in each nation, may be terminated one year after notice has been given to the other party. What counts as “notice" is unclear.

The Visiting Forces Agreement is seen as an official treaty in the Philippines because it was approved by the Senate, and as an executive agreement in the U.S. Either side can terminate it with 180 days notice given in writing to the other party.

The Enhanced Defense Cooperation Agreement is considered an executive agreement by both sides. It has an initial term of 10 years, though it will remain in force unless either side terminates it with a year’s notice given in writing to the other party.

4. Do Philippine lawmakers need to sign off?

Not necessarily. While the Philippine Constitution requires at least two-thirds of senators to approve an international treaty, it is silent on ending them. Pacifico Agabin, a constitutional expert and former dean of the University of the Philippines College of Law, said the decision to end a treaty is "completely within the discretion of the president." And the public for now seems behind Duterte: His approval rating hit 86 percent in a poll released on Wednesday.

5. Has this happened before?

The Philippines has periodically reassessed its defense relationship with the U.S., which ruled the nation as a territory for nearly 50 years until independence.

The Military Bases Agreement reached in 1947, originally a 99-year deal, was revised several times to give the Philippines increased economic compensation or sovereignty, including one amendment that called for it to expire in 1991.

In the early 1990s, leaders from both countries sought to extend the pact to allow the Americans to keep what was their largest military outpost in the Western Pacific. Yet an upswell of anti-colonial sentiment prompted the Philippine Senate to reject a fresh agreement, and the U.S. closed all of its bases by 1992.