Three years into his presidency, Rodrigo Duterte has escalated his confrontation with two forces at opposite ends of Philippine society -- the powerful Catholic Church hierarchy and the country's communist rebels.

He has directly threatened priests, ubiquitous in a largely Catholic country, while also calling for the military to "pulverize" the small bands of communist fighters who have a long-lasting low-level guerrilla campaign in the jungles of Mindanao island.

The church and the communists have in their different ways been a challenge for successive presidents. But Duterte's unyielding approach, which contrasts sharply with the more flexible politics of his recent predecessors, is pushing his ideologically diverse critics into unlikely alliances ahead of 2019's midterm elections for seats in the senate, the legislative upper house.

His latest assaults come amid critics' concerns over intensified crackdown on suspected drug users and traders, journalists, liberal activists and opposition leaders. The controversial president, who overturned conventions from the moment he took office (and even before when as a provincial mayor), seems to be dispelling any hope that he might relax once he was accustomed to power.

To implement sweeping political reforms, including a proposed constitutional change, Duterte, whose allies dominate the lower house of Congress, needs to secure control of the Senate, which is more powerful.

The president still enjoys strong support from loyal followers in the lower house, the Supreme Court and many in the business elite. His net approval rating is down from a sky-high initial 90% to the mid-50s%, but that is still high, especially for such a divisive figure.

But now he faces the prospect of a cross-ideological opposition alliance, which only needs to come of the election as the largest single force to frustrate Duterte.

Earlier this month, the Filipino leader expressed his exasperation with the Catholic Church, which has criticized his drug war that has reportedly claimed the lives of thousands of suspected drug dealers.

In a major break from his predecessors, who never dared to directly threaten the Church, Duterte went so far as declaring, "these [critical] bishops, kill them, those fools are good for nothing. All they do is criticize."

Presidential Spokesman Salvador Panelo quickly dismissed Duterte's threatening as remarks "hyperbole," which was only meant for "dramatic effect."

But Human Rights Watch condemned Duterte's threat against priests, since it's "clearly inciting people to commit violence against critics of the government."

2018 has seen unidentified gunmen killing three priests across the country, some of them while delivering religious services. Another priest barely escaped his assassins.

The killings have outraged the Catholic hierarchy which declared: "They are killing us, the shepherds. They are killing our faith. They are cursing our church." But no one has yet been held accountable for the deaths.

Duterte's escalating tensions with the Catholic Church has coincided with an intensified crackdown on communist rebels, progressive-leftist activists, and their alleged sympathizers.

Established in the 1960s, the Philippines' communist movement reached its heyday, fielding tens of thousands of fighters and hundreds of thousands of sympathizers, during Ferdinand Marcos' long dictatorship.

In recent years the rebels are reduced to only a few thousand scattered fighters. But they still have widespread support among progressive-leftist groups and marginalized people resisting extractive industries.

After initially endorsing peace talks with the rebels, Duterte in 2017 reacted to a breakdown in negotiations by launching a "Duterte Death Squad" to hunt elite rebel units and calling for the elimination of the insurgency before his term ends in 2022. Defending themselves in sporadic fights, the rebels are on the defensive, facing mass arrests and defections.

But Duterte's all-out offensive could spark a backlash by pushing together opponents into a loose alliance ranging from right to left and including the conservative religious hierarchy, priests, progressive-leftist groups, the liberal media and intelligentsia, human rights activists, left-leaning legislators and even disgruntled business leaders.

Both the Church and progressive-leftist groups have significant material resources and mobilizing power that can be used to support opposition candidates this year, in what will likely be among the most expensive and contentious elections in Philippine history. The Church gathers millions for Mass every Sunday. The leftist groups also reach huge numbers: for example, Akbayan, a social democratic movement, won a Senate seat for one of its representatives, Risa Hontiveros, who garnered close to 16 million votes in 2016.

Admittedly, ideological and tactical divides so far seem to have prevented the formation of a formal alliance. So perhaps does concern that declaring an outright "red-yellow" alliance could in be risky as it could be used as a pretext by Duterte to declare nationwide martial law. More likely is low-key cooperation among Duterte's critics.

Still, the Catholic Church adds legitimacy to this sort of operation, having been a pivotal player in Philippine politics for decades, notably in the "People Power" revolts against former presidents Ferdinand Marcos and Joseph Estrada.

The rise of evangelical groups, some of which openly support Duterte, has diminished the Catholic Church's dominance. Yet, according to the annual Philippine Trust Index, which measures confidence in social institutions, religious bodies, including the Catholic Church, enjoy the highest trust levels.

The opposition's hand is strengthened by widespread public disaffection amid the Philippines' recent economic troubles, including slowing growth and rising inflation.

As Duterte knows well, the opposition does not need to win to frustrate his plans to change the constitution to enhance his central authority. It just needs to secure more than a third of Senate seats. According to the constitution, constitutional revisions require the consent of two-thirds of legislators, in each of the Congress and the Senate.

Duterte could try to divide and conquer, handing out tactical concessions to each opposition group, to drive a wedge among ideologically diverse camps. He could, for instance, work with the Church to come up with a more humane joint campaign against illegal drugs and cease issuing open threats against priests. As for progressive-leftist groups, he could restart deadlocked peace negotiations between the government and the communist rebels.

Meanwhile, he could shore up his public support by improving macroeconomic conditions before the vote.

With his approval ratings still robust and key sections of the political elite staying loyal, the president has so far stuck to his guns, showing little appetite for compromise. The next few months will show whether bishops, liberals and communists will change his mind.

Richard Heydarian is a Manila-based academic, columnist and author; his latest book is "The Rise of Duterte: A Populist Revolt Against Elite Democracy."