Turkey and the European Union have spent three decades trying to unite, but the EU membership talks seem to be moving toward a permafrost that would effectively end a project that was as majestic as it proved elusive.

After the 28-nation EU gave the referendum victory of President Recep Tayyip Erdogan the frostiest of receptions and even questioned its legitimacy, the president took a step that may have been one too far: talking about reinstating the death penalty.

"Not only is this a red line, this is the reddest of all red lines," EU spokesman Margaritis Schinas said Tuesday. The death penalty is outlawed in all EU nations and is a key moral benchmark of the bloc.

"Moving from rhetoric to action on the issue of the death penalty would be a clear signal that Turkey does not want to be a member of the European family," Schinas said.

The previous evening, Erdogan, celebrating his referendum win, made that signal very clear.

"Our concern is not what George or Hans or Helga says. Our concern is what Hatice, Ayse, Fatma, Ahmet, Mehmet, Hasan, Huseyin says," Erdogan said as the crowd chanted for the return of capital punishment. "What Allah says. That's why our parliament will make this decision."

With such religious references, he also touched upon the divide that has long kept both sides apart. The European Union which swelled during the courtship with Turkey to 28 nations and 500 million citizens, had always been seen as a Christian club, while Turkey is an overwhelmingly Muslim nation of 80 million.

Still, opposites attracted and the economic boon for both sides was long too much to resist. Together in the EU, the reasoning went, they'd be much stronger to face globalism and increase wealth for both sides. Politically, Europe would stretch its clout right up to the borders of Iran, Iraq and Syria.

Turkey applied to join the EU three decades ago, and they started negotiating in 2005. But of the 16 negotiating chapters on issues as varied as capital movement and food safety, only one has been provisionally closed — science and research. In short, it hasn't worked out.

"It was not a very realistic prospect," said Amanda Paul, Senior Policy Analyst at the European Policy Centre.

Over the past years under Erdogan, relations have been progressively under pressure as the emboldened Turkish leader expanded his reach of power, even though the EU did clinch a deal with Erdogan to keep refugees in Turkey in return for billions of euros in aid.

The suppression of the coup attempt last year was widely criticized in Europe as a move toward authoritarianism.

As the referendum to greatly expand Erdogan's might drew near, relations got worse. The Turkish leader was looking to immigrants in EU nations to make a difference in a tight race. When EU nations like Germany and the Netherlands balked at turning their territory into electoral stomping grounds for Turkish officials backing Erdogan, he accused them of acting like Nazis.

With each passing month, the prospect of adding Turkey as an EU member seemed to be retreating.

When monitors from the Organization for Security and Cooperation in Europe questioned the results of Sunday's referendum and said there were several circumstances in Turkey undermining important election safeguards, the EU — unlike U.S. President Donald Trump — felt it could not immediately endorse the outcome, let alone congratulate Erdogan.

On Tuesday, the EU called for Turkish authorities "to launch transparent investigations into these alleged irregularities found by the observers."

Analyst Paul said it no longer matters much at this stage.

"We have seen already the narrative from President Erdogan who said he does not care anyway what the EU or anybody else says."

Now, the prospect of the restoration of the death penalty sounds perhaps the death knell for the negotiations.

"If they were to bring back the death penalty it would be very difficult for the EU not to suspend the accession process," said Paul. "But I mean, that said, we have to remember that this process is basically ... dead almost since the day it was launched back in 2005."


Sylvain Plazy in Brussels and Elena Becatoros in Istanbul contributed to this report.