BERLIN — Rest is short-lived in politics.

Here in Germany, the Social Democratic Party (SPD) knows that well. And Chancellor Angela Merkel is about to feel it too with incoming French President Emmanuel Macron. But she also knows everything in politics can change in a day.

Macron's party, recently renamed La République En Marche, has to demonstrate in the French parliamentary elections in June that it is more than just a tripwire for Marine Le Pen's ambitious bid to the presidency.

Macron is seen as a savior of the political center who rose from nowhere and promises to do everything differently. Yet saviors and their ad hoc parties often disappear as quickly as they came. There is no core electorate, no stable body of financial functionaries, no tried-and-tested political program, no trust without constant reassurance, no sense of belonging. The National Front, instead, has all of that.

For the crucial National Assembly elections next month, Macron has announced that La République En Marche would have a candidate in every district and that those who join the party from other political factions would have to run under the new list's ticket. The stakes are high: Macron's ability to integrate players from various parties into his movement will be clearly measurable in the results of the parliamentary elections on June 11 and June 18. He might get an absolute majority in those elections, too, but he might also be forced to form a coalition with one of the displaced traditional parties to obtain a majority.

The National Front might become a powerful opposition force, and though Macron might try to label it an "old party," that won't necessarily stick. The National Front could become the voice of those seeking a familiar, tangible alternative, should Macron's movement disintegrate amid diverging political views. No, Marine Le Pen's tenacity should not be underestimated.

Election days quickly fade into oblivion, moods change and trying to jam through reform could lead to Europe breaking apart.

Merkel has had her fair share of experience with politically divergent groups while dealing with Italy and Greece. So far, she has managed to satisfy her electorate without offending her European partners — including Greece. Greek Prime Minister Alexis Tsipras has lasted as long as he has partly because he could always count on Merkel keeping her word, especially about Berlin's red lines.

France, of course, is an entirely different matter. Macron saved the European Union all on his own with enormous political courage. The French part of the European engine may finally kick in again, but for this to happen Macron needs tangible success. And the election cycle is unrelenting. The European Parliament elections are set for spring 2019, not so far off in political terms.

These will set the stage for another standoff between Macron and Le Pen. Unfortunately, from Merkel's point of view, Macron has promised to reform the eurozone. It is unfortunate because the European Union treaties will have to be altered and Merkel has warned that this would be difficult. A large reform such as the creation of a eurozone budget or the naming of a joint eurogroup finance minister would require careful, long-term preparation.

Macron has vowed to accomplish this within five years, a highly ambitious goal. Merkel will most likely tell him that, while they all want to achieve such reform, it cannot be done overnight just because more than 66% of the French electorate voted for him one Sunday.

Indeed, election days quickly fade into oblivion, moods change and trying to jam through reform could lead to Europe breaking apart. Brexit, Greece and Turkey (including the often underestimated Cyprus debacle) are difficult and critical enough without added stress on the European political dynamic.

But Macron will be in urgent need of success, of maintaining the momentum of his popular mandate. Otherwise, he may wind up becoming a "president on call," just like François Hollande. Will Merkel let this happen with Germany's top European partner? The chancellery minister Peter Altmaier already hinted on Sunday that Berlin, at least in the foreseeable future, intends to not take the euro deficit limit at face value. So, even if there won't be an immediate EU reform, Macron will at least be allowed to ignore the upper debt limit of the Maastricht treaty due to the "extenuating circumstances' of his national reforms. This exception could enable Macron to boost state investment in France, knowing that Germany won't constantly be reminding France of the debt limit restrictions.

Macron wants to, once more, make France the poster boy of the eurozone stability pact which in turn makes German leniency politically justifiable. The same may apply to EU programs for digital infrastructure or fighting youth unemployment. Germany could notably increase its EU payments, which would become easier and easier for Merkel to justify the more Macron drives internal French reforms forward.

Merkel has bigger internal political fish to try than Macron.

But, on the other hand, Merkel has her own election calculations to consider. Prior to the German parliamentary elections next fall she cannot be seen as diluting the principles to which she previously adhered to. In the face of German voters, there can be no communal sharing of debt and cooperation with troublesome EU partners. Otherwise Merkel would lose the trust of certain parts of the electorate and could get into trouble with the Federal Constitutional Court, which passed very strict regulations in 2011 and 2016 on German Federal policies regarding EU debt management.

If Merkel were to be remain Chancellor of a large coalition government after Sept. 24, 2017, she would have to face the regional federal state parliamentary elections in Lower Saxony in February 2018 as well as those in Hesse and Bavaria later that year. The regional federal state parliamentary elections in Bavaria would be of special significance to Merkel in view of the then looming EU elections. Merkel has bigger internal political fish to try than Macron until the EU elections and that should be kept in mind in regards to German-French relations.

Still, both Merkel and Macron face the shared challenge of elections in other EU countries, such as the Czech Republic, where a national populist party is gaining momentum, or Italy, where candidates of the political middling ground and the populists are head-to-head in the polls. There is also Austria, where the electorate will choose its own next chancellor in 2018, and where the far-right Freedom Party could win. Now that would be something. But since last Sunday, at least, there is the prospect that a certain German-French duo could be so successful in the meantime that the EU will no longer seem like a club of the helpless that Angela Merkel is desperately trying to hold together all by herself.