Manila, Philippines - What if Philippines President Rodrigo Duterte called US President Donald Trump a "son of a whore" or a "faggot"?

Duterte aimed those words at Trump's predecessor Barack Obama and Philip Goldberg, then US envoy to the Philippines, respectively, after they criticised his "war" on illegal drugs. At least 6,000 people, mostly drug suspects, have been killed by either police officers or vigilantes in Duterte's controversial flagship policy.

The vulgar name-calling is unlikely to continue when Duterte hosts Trump here starting on Sunday, along with more than a dozen other heads of state, for a series of meetings with the Association of Southeast Asian Nations (ASEAN). The two leaders are scheduled to talk face-to-face for the first time, and their meeting is highly anticipated - at least by Filipinos.

The one-on-one comes at a crossroads in the relationship between their countries. Duterte has been pushing for an "independent foreign policy" that has him courting China and Russia while creating some distance from a longtime ally, the US, at least in terms of rhetoric.

Trump, on the other hand, has all but pivoted from Obama's "rebalance to Asia" choosing to put "America first" in both trade and security, to the chagrin of its developing economic and strategic partners such as the Philippines.

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More than pleasantries

The two men got on well from the first time they talked on the phone in December of 2016, Duterte congratulating Trump on winning the election, Trump praising Duterte for fighting illegal drugs "the right way". But when they sit down for this long-awaited talk, they will have a lot more in mind than exchanging pleasantries.

For Trump, it will be "all about North Korea and, to a less degree, trade deficits", said Gregory Poling of the Washington-based Center for Strategic and International Studies.

"And no matter who the president meets with … it seems like every meeting has to be about North Korea first and last," Poling told Al Jazeera.

Duterte, this year's ASEAN chairman, certainly shares Trump's concern over North Korea's nuclear weapons programme, and he has led ASEAN in condemning Pyongyang's provocative actions. He also promised Trump in a phone call last April that he would urge China President Xi Jinping to rein in North Korea's Kim Jong-un.

But Duterte knows his country is not a primary target of Pyongyang's nukes, and while he does not seem inclined to push strongly for anything in particular during the ASEAN meetings (he had, in fact, wondered whether he should call them off), there is one thing he vowed to protect - even against Trump: his war on drugs.

'Not your business'

"Lay off. That is not your business. That is my business," Duterte said he would tell Trump or any leader who questioned his policy, as he embarked on a trip on Wednesday to Vietnam, where he and Trump attended the Asia-Pacific Economic Cooperation summit.

Although it is unlikely that Trump will, of his own volition, bring up the issue of human rights violations with Duterte, there is a push from others in the US government to do so, particularly from Congress.

"We can expect that the two leaders will be open and frank with each other. Important developments in the Philippines and in the United States, a full range of issues will be discussed," said Sung Kim, Washington's envoy in Manila, in a recent forum with reporters.

"I think Secretary [of State Rex] Tillerson and other senior officials in Washington have made it very clear that human rights, rule of law, due process - these are very important principles and values that the United States continues to hold very dear," Kim said, adding the US will continue to work with allies such as the Philippines on those matters.

However, in the two phone conversations Trump has had with Duterte, he congratulated the "good man" on the drug war, for which both leaders drew strong criticism.

Natural affinity

The two politicians share many similarities. They both built their election campaigns on populist promises, presenting themselves as strongmen who would override stuffy bureaucracy to bring about quick and drastic changes "for the people".

Both leaders have been accused of breaking laws and violating peoples' rights - as in Trump's immigration ban and Duterte's drug war. They have both drawn flak for supposedly selling out to another country: Trump to Russia for his election, Duterte to China in a sovereignty dispute over the South China Sea.

And there is, of course, their way of communicating in public. They "say it like it is" - unedited, uncouth and, at times, unverified - which endears them to their supporters, but earns them critics at the same time.

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All these may explain the natural affinity between Duterte and Trump. But when they meet in Manila, they will have real issues to deal with, and while their friendly rapport will certainly help their conversation, it will also be tested.

The US needs its former colony to round up ASEAN to exert whatever pressure it can against North Korea. The Philippines needs its former coloniser to keep sending military and economic aid, but wants it to back off from its domestic affairs.

And then there is China - challenging the US as a traditional Asia-Pacific power and pushing against the Philippines' maritime borders in the South China Sea.

Washington is waiting on Manila to flesh out a deal to give US troops access to a number of Philippine military bases, while Manila is counting on Washington to help beef up its defence capabilities in the face of an increasingly dominant Beijing.

Larger powers

With leaders from larger powers present in the meetings, the danger is that the individual concerns of the ASEAN states might fade into the broader agenda of their more influential visitors.

"The South China Sea is not Donald Trump's issue," Poling said.

But if Duterte's main concern is his drug war, then a preoccupied Trump won't bother him.

"The problem is that Trump - in his desire to bring the Philippines to adopt a strong anti-North Korea position - might in effect inadvertently legitimise or gloss over Duterte's drug war," said Jose Antonio Custodio, a security analyst based in Manila.

"That will, of course, result in more abuses," he added.