It's a relationship that has had its rows and rocky periods, but after five years as the couple in charge of the European Union, Donald Tusk and Jean-Claude Juncker will no doubt leave with a sigh of relief that the EU show is still on the road. Even if one of the lead players wants to leave.

Five years ago, the picture was very different. Juncker talked of leading "a last-chance commission," when he addressed the European parliament as the body was seen to be losing its relevance and struggling to find a role.

He warned then that the European bodies including the Commission and the Parliament either had to bring together the peoples of Europe or, he said, we will fail.

Ironically, analysts in Brussels believe it has been the biggest headache of their term – Brexit – that has helped to forge a greater unity among the other 27 countries. Because the three-and-a-half years of still unresolved discussions have proved so fraught, there is much less talk of others wanting to leave.

At the outset, it was far from clear that the two could prove to be an effective leadership duo. Tusk was the action man, former prime minister of Poland with an appetite for hard work, a pragmatic outlook and a rather dour personality.

Juncker arrived as the former prime minister of Luxembourg, who had presided over many of the favorable tax deals enjoyed by the very global technology companies he now had the job of policing. He was the bon vivant with an appetite for good food and wine.

But it was not just their personalities or lifestyles that were at odds, they were fundamentally divided on the future direction and core values of the EU and its key institutions.

Tusk promoted the view that it was the nation states that were the members of the European club and that were the drivers of change. He believed it was the governments of the member countries that had to take the lead on the policies and principles that governed the future of the bloc.

Juncker took a markedly different view. He argued the bloc had for far too long been dominated by narrow national interests that had served to boost populism throughout Europe. He insisted that a more overtly political commission and parliament would help to address the problem, not exacerbate it by bringing the European institutions closer to the electorate.

A degree of success

At the end of the five-year term, analysts believe both of them can claim a degree of success. Although, equally, there has been no fundamental power shift within the EU institutions and the balance between the three remains largely unchanged.

The European Council remains the EU's supreme political body, bringing together the leaders of the member states at least every three months to set out general policy objectives and trouble-shoot in areas where ministers cannot agree.

The European Commission is part political and part administrative, carrying out four key functions: it proposes legislation, it manages policy and the budget, it acts as guardian of the treaties and it represents the EU in external trade relations. If and when the UK leaves the bloc, it will be the Commission's trade representative Phil Hogan who negotiates a new deal.

In the end, analysts here agree it won't be the clashes Juncker and Tusk have had over policy or principles that will be remembered. The defining issue of the past five years will be the conduct of the grueling and often divisive talks over the UK's vote to leave the EU.

Three-and-a-half years of discussions, led by the EU's chief negotiator Michel Barnier, have produced a non-negotiable deal, followed by talks on a second non-negotiable deal, three consecutive delays to the date for Britain to leave and, frustratingly, as the Tusk/Juncker show leaves the stage, no final resolution.

Brexit frustration

The frustration of both men has shown clearly, particularly in the latter stages of the process. In February 2019, after meeting the Irish Prime Minister Leo Varadkar, Tusk gave vent to his true feelings when he said: "I've been wondering what that special place in hell looks like for those who promoted Brexit without even a sketch of a plan on how to carry it out safely."

Juncker saved his remarks for October 2019, when he addressed the European Parliament in a weary and irritated tone of voice: "It has pained me to have spent so much of this mandate dealing with Brexit, when I have thought of nothing less than how this Union could do better for its citizens. Waste of time and waste of energy."

It seems very unlikely he is going to change that view as he steps out of the car and hands the steering wheel to his successor Ursula von der Leyen on 1 December – a month later than planned.

As for Tusk, when he hands over to the former Belgian Prime Minister Charles Michel as president of the European Council, he will remain in the mainstream of European politics as head of the main European parliamentary group, the European Peoples Party.

New leadership, same old problems.