The prospect of a triumphantly re-elected Recep Tayyip Erdoğan armed with sweeping new presidential powers is deeply alarming to many Turks, but it is also a scary prospect for the international community. Since taking national office 15 years ago, Erdoğan has turned from neighbourhood bully-boy into geostrategic threat. Under his choleric, resentful tutelage, Turkey has ceased to be a reliable friend of Europe and the US. If he gets his way in Sunday’s polls, Erdoğan, a dictator in all but name, is likely to foment further instability in Syria and throughout the Middle East region.

Latest estimates suggest Erdoğan, who is facing stronger than expected opposition, will be forced into a second round run-off in July. Likewise, his neo-Islamist Justice and Development party, in power since 2002 and accused of economic mismanagement and corruption, may lose its overall parliamentary majority.

Few observers believe Erdoğan will ultimately be denied the presidential palace. Despite his egregious abuses of civil and human rights, the mass arrests that followed the failed 2016 coup, and his contempt for Turkey’s secular democratic institutions, including independent media, Istanbul’s former mayor remains a potent force.

Erdoğan’s personalised politics, underpinned by support from nationalists, observant Sunni Muslims and rural conservatives, and sustained by deliberately divisive, populist policies, represent a big challenge for foreign partners.

Ahmet Davutoğlu, an amiable professor who was Erdoğan’s chief adviser, foreign minister and prime minister from 2003 to 2016, helped promulgate a “zero problems with neighbours” foreign policy that initially brought positive regional advances. So-called “neo-Ottomanism” was, briefly, all the rage.

But as Davutoğlu’s influence faded, Erdoğan – always quick to imagine a slight or find a grievance – reversed course. Relations with Egypt, a key Arab power, are a case in point. Erdoğan’s ambition to be a leader for the entire Muslim world climaxed in September 2011 when he visited Cairo shortly after the Arab spring revolt that toppled Hosni Mubarak. He was feted as a hero.

But when Mubarak’s Muslim Brotherhood successor, Mohamed Morsi, was ousted by a military junta, Erdoğan all but declared war. “Either Bashar [al-Assad, Syria’s president] or [Egyptian army chief Abdel Fattah al-] Sisi, there is no difference between them,” he declared in 2013. “I am saying that state terrorism is currently underway in Egypt.”

By creating notional national enemies, Erdoğan wins votes, or at least he thinks he does. Photograph: Huseyin Aldemir/Reuters

Erdoğan is still bent on creating a new Ottoman sultanate. But his idea is a far cry from the benign construct envisaged by Davutoğlu. On the contrary, it thrives on problems with neighbours. The rift with Cairo endures. And Erdoğan has also fallen out with the Gulf monarchies over continuing links to the Muslim Brotherhood, Ankara’s perceived military ambitions, and its de facto alliances with Iran and Qatar. Prince Salman, the Saudi crown prince, says Turkey is part of a “triangle of evil” that includes Iran and Islamic extremists.

As a politician feeding on friction and strife, such divisions are grist to Erdoğan’s mill. By creating notional national enemies, he wins votes, or at least he thinks he does. Thus the current election campaign has seen escalating Turkish military operations inside northern Iraq, on the Kandil mountains border with Iran, where the outlawed Kurdish group the PKK is based. Neither Tehran nor Baghdad has given permission for these dangerous armed encroachments – but, in his hubris and arrogance, Erdoğan does not care.

According to the Turkish army, dozens of PKK militants were “neutralised” in Iraq and south-east Turkey this week alone. Such random violence is entirely typical of Erdoğan’s crude overall approach to the “Kurdish problem”, which he in any case claims, preposterously, to have solved. Kurdish civilians bear the brunt of his failure. Pro-Kurdish politicians, such as his presidential rival, Selahattin Demirtaş, campaigning from behind bars, end up in jail – or worse.

Erdoğan’s Kurdish obsession is exacerbating conflict along the Syria-Turkey border, too. The decision earlier this year to invade Afrin, in north-west Syria, was dictated by his wish to repulse pro-western Syrian Kurdish forces, not to help US and allied fighters combat Islamic State or assist anti-Assad rebels.

To avert a military clash between US and Turkish forces around Manbij, the Trump administration shamelessly instructed the Kurds, its only reliable local allies, to surrender a town they had bravely liberated from Islamic State.

The pattern repeats around the region. Erdoğan has picked a fight with an old enemy, Greece, in recent weeks, sending aircraft to buzz Greek islands after Athens refused to hand over suspects in the 2016 coup. This confrontational behaviour has brought talk of war – a not wholly improbable outcome, given the escalating dispute over energy exploration rights off still-divided Cyprus.

Similarly, past attempts to improve relations with Israel have been abandoned in favour of resumed, politically expedient enmity, justified most recently by Erdoğan’s claim to care about dead Palestinians in Gaza.

The overall picture reflects a broader deterioration. This week the US Senate tried to block the big-ticket sale of F-35 fighter jets to Turkey after members of Congress accused Erdoğan of “actively operating to undermine US interests around the world”. Turkey, they said, “has made a common practice of aggressively targeting US allies while aiding and abetting our adversaries”. That’s an extraordinary way to talk about a Nato ally.

Likewise, Erdoğan’s damaging rows with European countries over refugees and future EU membership, his brute defiance of human rights norms and shared democratic standards, and his growing military collaboration with Vladimir Putin, symbolised by the purchase of advanced Russian S-400 missiles, seem certain to get worse if he wins a new five-year term. Turkey’s voters have a duty to the world, not just to themselves. Kick him out.

• Simon Tisdall is a foreign affairs commentator