The Philippines has taken a fateful step toward establishing authoritarian rule with the controversial ousting of the Supreme Court chief justice -- as a once-thriving democracy relentlessly turns into an imperial presidency.

Maria Lourdes Sereno was among the few remaining voices of independence in the Philippine state, rarely shying away from confronting Philippine President Rodrigo Duterte's perceived assaults on rule of law.

In response, the tough-talking Filipino president has openly called for her dismissal in recent months. In a potentially unconstitutional move, the country's highest court narrowly voted (8-6) to unseat the chief magistrate on a motion filed by the solicitor general.

The controversial court ruling, published on May 11, immediately provoked an outcry, with leading legal experts as well as prominent legislators -- including some Duterte allies -- questioning its constitutionality. As a result, the Philippines faces a de facto constitutional crisis, which weakens its democratic institutions and undermines overall confidence in the rule of law.

Critics lambasted the high court, claiming that it irrevocably undermined its credibility and yielded its institutional independence. Instead of rule of law, undergirded by impartial and credible institutions, the Philippines is gradually embracing rule by law, where constitutional matters are increasingly shaped by balance of political power.

As many as 14 senators, who constituted the majority in the upper house of legislature, have signed a resolution, which calls on the Supreme Court to reconsider its decision. The list includes independent senators, who at times have been supporters of Duterte's key policies, such as Sherwin Gatchalian, Grace Poe, Joel Villanueva Sonny Angara and Loren Legarda. Other senators, who are fully allied with the president, are expected sign the resolution soon.

No less than Senate President Aquilino Pimentel III, a staunch Duterte ally, drew the line by arguing, "in impeachment matters ... the Senate is the one and only impeachment court."

The Senate leader lambasted the high court's decision as "a very unusual remedy," on which "the esteem" of the magistrates is anchored. The dissenting justices also similarly questioned the validity of the ouster, with some implying that personal rivalries and deference to the president could have played a role in the controversial decision.

In another unprecedented move, some opposition lawmakers have gone so far as calling for the impeachment of the eight justices that voted in favor of the motion. The Integrated Bar of the Philippines (IBO) along with other leading legal experts has rallied behind appealing to the Supreme Court to revisit its own ruling, openly questioning the decision's its constitutionality.

The Philippine Constitution (Section 2, Article XI) states, "Members of the Supreme Court ... may be [author's own emphasis] removed from office on impeachment for, and conviction of, culpable violation of the Constitution ... ."

In its decision, the Supreme Court contends that the word "may" denotes the presence of alternative mechanisms for unseating a magistrate for any impeachable offense. In other words, the bench can dismiss one of its members even without an impeachment process.

In particular, the 153-page ruling maintained that, the constitution allows such actions since it is "predicated on grounds distinct from those of impeachment."

But beyond the fine legal debates -- rich in semantics and couched in high-minded language -- what is at stake is no less than the soul of the Philippine democracy.

What we are beginning to witness is the disturbing phenomenon of "rule by law" instead of the "rule of law." Those in power are determining the interpretation as well as application of the constitution. To critics, institutional deference, rather than defiance, has already shaped all major Supreme Court decisions under Duterte.

In the past two years, the country's highest court cleared the controversial burial, upon the president's request, of former Filipino dictator Ferdinand Marcos in the cemetery of nation heroes.

It also cleared the president's unilateral declaration (in potential violation of the constitution) of Martial Law in Mindanao early last year. It even gave Duterte the ultimate discretion to decide upon its temporal and spatial application.

Up until today, an indefinite Martial Law is in effect throughout the entire southern island, even if Islamic State-affiliated elements only managed to lay siege on and threaten Marawi City and nearby provinces. By October last year, the siege was actually over.

Sereno consistently remained among the few dissenting justices, who opposed erosion of rule of law under the proto-authoritarian president. She has openly criticized Duterte's signature policy, namely his war on drugs. "[W]e have to face the reality of the daily accounts of unsolved killings, many of them committed brazenly, with the public warnings against drug pushing or addiction," she warned more than a year ago at the height of Duterte's war on drugs. "[T]he perception of the rule of law in our country has swung from marked improvement to a downgrade."

It's hard to imagine the Supreme Court's latest controversial decision to oust Sereno was devoid of broader political calculation. Last month, Duterte openly threatened the newly-ousted chief justice, stating "I am putting you on notice that I am now your enemy," and openly called for her "forced removal".

For months, Duterte's supporters questioned Sereno's psychological capacity to lead one of the top offices in the country, while claiming she wasn't transparent with her income and wealth prior to her assumption of office. Some of the justices who voted against Sereno earlier testified against the chief magistrate, questioning her integrity and legitimacy to oversee the judiciary. The justices later refused to recuse themselves in voting on her ousting, despite having previously expressed their prejudices against her.

Duterte's allies in the House of Representatives, where he has a super-majority support, quickly moved to recommend the impeachment of the chief magistrate. Yet, the Senate, which is occupied by large number of independent and opposition legislators, remained largely skeptical, if not opposed.

Calculating the likely failure of a full-fledged impeachment trial at the Senate, the government's chief prosecutor, Jose Calida, opted for the unconventional approach. The solicitor general sought the unseating (rather than impeachment) of Sereno by filing a motion of quo warranto, which questions the very legitimacy of an official occupying an office. The gamble paid off.

Duterte may have got what he wished for, but the victory comes at the expense of the country's democratic health as well as economic wellbeing. The ongoing constitutional crisis will not only undermine confidence in the country's institutions but unsettle, especially investors and international economic partners. The Southeast Asian nation, long a bastion of democracy in the region, is now in a constitutional crisis with no clear way out.

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