He has vacillated on his stance toward US-Philippine ties, alternately repudiating the Obama administration and embracing Trump.
Domestically, he has gone back and forth on the issue of martial law, repeatedly suggesting imposing it before backing off.
Duterte returned to the subject this week, bemoaning the constitutional limits on how the Philippine president could deal with security threats like war.
"If you have martial law, only one person should be in control," Duterte said during a visit to the northern Philippines on Thursday.
"If there's invasion or war and I declare martial law, I cannot proceed on and on to deal with the trouble as I still have to go to Congress, go to the Supreme Court," he added, according to AFP. "That's why that needs to be replaced."
Under current Philippine law, the president can declare martial law for up to 60 days, but within 48 hours he or she would have to submit a report to the congress, which could then revoke it. The Supreme Court can review the declaration's legality and must issue a decision within 30 days.
Those restrictions were put in place with a new constitution written in 1987, a year after millions of Filipinos went into the streets to demand dictator Ferdinand Marcos be removed from power in a movement called the "People Power" revolution.
Marcos imposed martial law from 1972 to 1981 to fight crime and a communist insurgency, but governments since have said thousands were killed and tortured during Marcos' reign.
The Marcos legacy makes martial law an incendiary topic in the Philippines, and Duterte — who has repeatedly inveighed against a wave of crime and said human rights would be an afterthought if ISIS arrives in the Philippines — has raised alarm by flirting with it.
In March, then-President Benigno Aquino said Duterte's campaign promises would put him a step away from being a dictator. Duterte repudiated that charge by invoking his mother's experiences under Marcos.
Bonifacio Ilagan, who was jailed and tortured during Marcos' martial-law period, told AFP that Duterte's references to martial law could be a "trial balloon" in order to assess public opinion as a prelude to making moves to amend the constitution.
Duterte has allies who control the country's congress.
They have backed his proposal to bring together a "constitutional assembly" to change the centralized government to a federal one prior to the end of his term in 2022, according to AFP.
Ilagan said that assembly would have the power to amend the president's martial-law powers, but he cast doubt on how that would be received.
"I honestly believe the people will resist," he said.
Despite the controversial context of Duterte's martial-law musings, they have mostly remained in the background amid his ongoing battle against the drug trade in the Philippines.
Since he took office in July, about 6,000 people have been slain in drug-related killings — only about two-thirds have been in police operations, raising fears of vigilante activity or of an extrajudicial-killing campaign.
The vicious crackdown Duterte has inspired and the harassment his critics have faced lead some to suggest that while there is no de jure declaration of martial law, it exists in de facto status.
"It is not necessary that you have a declaration of martial law to have martial law," Bishop Broderick Pabillo, who works in the northwest Manila slum of Tondo, where many drug suspects have been killed, told AFP.
Duterte may back off his Thursday comments in the coming days, as he has done several times in the recent past. But his wavering is no comfort for some of his countrymen.
"He said a few days ago that martial law was stupid and didn't work, and yet now he says something else," Sen. Francis Pangilinan, a critic of Duterte, told AFP. "His lack of clarity is a serious cause for concern."