"We failed miserably as a party," Arne Lietz has told DW's Michel Friedman.

In an exclusive interview on Conflict Zone the day after the German election results, the SPD MEP said, however, "Who knows what would have happened if [Schulz] wouldn't have run the campaign."

Schulz, a former European Parliament president, failed to convince German voters he was a credible alternative to Merkel. Despite a significant bounce in the opinion polls following his announcement as the party's candidate for chancellor, the SPD received just 20.5% of the vote, down more than five percentage points from 2013.

But he has vowed to stay on as leader of the party, though not of the parliamentary group, saying he will attempt to lead its revival in opposition. Lietz rejected that Schulz should step down following the election disaster: "He should stay the leader of the party if he wants to be."

Schulz bounce falls flat

Lietz also resisted putting the blame on his leader, citing Schulz's early popularity in the polls: "We had a swing which was interesting last January where we were [level with] Merkel's party."

However, the party's failure to make Schulz a visible presence in regional elections in North Rhine-Westphalia has been criticized as a significant mistake.

"That has already been said, also by our party leaders, that that was a decision which was not the right one."

But Lietz was keen to support his leader's efforts during the election: "We still did very well with Martin Schulz as a candidate," the German MEP said.

Could the results then have been even worse without Schulz?

"That might be possible," Lietz told Michel Friedman.

Asked why Schulz didn’t do better, Leitz went on to say: "I don't have an idea yet. But we have discussed this in numerous situations if he should have made certain things more clear […] To run a European campaign as Macron did, much more forward. And Martin ran on European politics but I think after the change that Macron brought to France, also the situation from the European perspective, got a bit better that people saw that the pressure might not be as high.”

AfD gains a 'brutal disaster'

But the biggest story of the election was not the drubbing of the SPD or Merkel’s losses, but the rise of the far-right populists, Alternative for Germany (AfD).

Their election to the German parliament – for the first time and as the third largest party with 94 MPs – is "a brutal turning point for the country," said Lietz, who also sees the AfD’s anti-EU agenda as a serious threat: "The European Union as such is not a given. We have to fight for it every day."

Rule of law

And threats to the EU come not only from opposition parties within Germany, but governments on its borders. 

Poland and Hungary have caused rows with Brussels over accusations of anti-democratic behavior and the rejection of refugee quotas. The European Court of Justice recently upheld the EU's scheme to relocate refugees around Europe, challenged in court by Hungary and Slovakia. Meanwhile controversial judicial reforms in Poland have led European Commission First Vice-President Frans Timmermans to threaten using Article 7 in response.

As defined in the Lisbon Treaty, triggering Article 7 could lead to a member state losing its voting rights in the EU for breaching the founding principles of the union, quoted in Article 2 as "respect for human dignity, freedom, democracy, equality, the rule of law and respect for human rights."

Member states “have to take [Article 7],” said the German MEP, who wants to put as “high pressure as possible on these countries.”

Described by some as a "nuclear option", the Article 7 mechanism has never been used before.