EU leaders face difficult talks this week on the thorny issues of how to plug holes in the post-Brexit budget and choose a successor for European Commission chief Jean-Claude Juncker.
A special one-day summit in Brussels on Friday of the 27 leaders without Britain is meant to be a key step in the roadmap to a leaner and more unified bloc after Britain leaves in just over a year.
But cracks have already appeared between French President Emmanuel Macron, leading the charge for a reformed Europe, and Juncker with his federalist vision of how top EU officials should be chosen in future.
The row means the EU's attempts to overcome the shock of losing a major member are running into the classic problems that have bedevilled it for its six decades of existence: money and sovereignty.
Juncker was picked after European elections in 2014 by a controversial "Spitzenkandidat" system -- German for "lead candidate" -- under which the political group with the most votes gets to nominate its candidate for the job.
Both the European Parliament and Juncker back a repeat after the May 2019 European election, saying it gives the public a direct say in who heads the commission, the EU's powerful executive arm.
- 'Right and obligation' -
European Council President Donald Tusk -- who coordinates summits and represents the EU member states -- is expected to lay out options at the summit, including whether to continue with the Spitzenkandidat system.
Leaders are expected to say it is their own "right and obligation" to choose the commission chief, while "taking into account" the views of parliament, as the EU treaties state, an EU source told AFP.
Many national leaders are bitterly opposed to the Spitzenkandidat process, saying it sidelines democratically elected heads of government in favour of a backroom deal by Brussels-based political parties, and also makes the job of commission chief too political.
Macron this week slammed the Brussels establishment as ideologically incoherent and called for a "political revamp" to give the commission a clear mandate, defined by the national leaders.
Juncker however said earlier this week that the Spitzenkandidat system was "completely logical". He also called for the commission chief's job to be merged with Tusk's.
The row has become particularly fierce after the European Parliament earlier this month dealt Macron a slap by voting against "transnational lists" -- which would allow 30 of the 73 seats vacated by Britain to be elected on pan-European tickets, instead of directly to constituencies.
"Why should we have Spitzenkandidaten if we have no transnational list for elections?!" Luxembourg Prime Minister Xavier Bettel tweeted.
- Fixing a hole -
Filling the hole that Brexit leaves in the EU's multi-year budget from 2020 threatens to open up even deeper divisions -- but this time between member states themselves.
Tusk will ask the leaders at the summit whether they want to increase the budget, decrease it or keep it the same, sources said.
EU Budget Commissioner Guenther Oettinger has said that Britain's exit could leave a hole of as much as between 12 and 15 billion euros ($15-19 billion) and suggested that contributions be increased to between 1.1 percent and 1.2 percent of GDP from the current level of one percent of GDP in the 2014-2020 budget.
The Netherlands, Denmark, Austria, Sweden and Finland, all net contributors, are said to be against that idea.
Warnings by Oettinger of cuts on agriculture -- a bugbear for France -- and "cohesion funds" that benefit poorer eastern European states are also likely to go down badly.
But there is little appetite for suggestions that the EU could try to bring countries like Poland and Hungary into line on issues including the rule of law and migration by making cohesion funds "conditional" on good behaviour.
With these tensions in the background it is no surprise that the EU has been stressing the need for unity in Brexit talks with Britain.
Tusk is expected to ask leaders on Friday if they want to push ahead next month with issuing negotiating red lines on a post-Brexit future relationship with Britain.
Uncertainty over Britain's wishes, and difficulties in negotiations on a post-Brexit transition period, could push that back.