If the experience of socialists elsewhere in Europe is any indication, Spain’s should be wary of entering into a grand coalition with Mariano Rajoy’s conservatives.

Neither won an overall majority in Sunday’s election, leaving them either at the mercy of smaller parties on the left and right or forcing them — for the first time — into a government together.

A pact between Rajoy’s People’s Party and the Socialists would be the only one that can easily command a majority in the new parliament. But it would mean a radical break with the past — and could spell doom for what is still Spain’s largest left-wing party.

Left-wing challenge

The Socialists won ninety out of 350 seats on Sunday, an historic low and only 21 seats ahead of the anti-establishment Podemos party, which didn’t exist four years ago.

Podemos appealed to young and leftist voters who see the Socialists as part of the old establishment. The latter have alternated in power with the People’s Party since democracy was restored, but never governed together. Both have seen their share of corruption scandals through the years. Seven years into an economic malaise that started when the Socialist were last in power, neither can claim to be exceptionally competent either.

The national interest argues for a grand coalition. The alternative is a minority People’s Party administration that could be voted out at any time or a broad left-wing alliance, including Podemos and the communists, that probably wouldn’t last much longer.

Rajoy’s conservatives, who had an absolute majority in the last parliament, also have a clear political interest in such a deal: it would almost certainly shrink the Socialists further and leave them as the only serious party of government.

Cautionary tales

The Socialists know it and that’s why they’re ruling out keeping Rajoy in power.

They can cite what has happened to socialists in Germany and the Netherlands to justify rejecting a left-right pact.

In both countries’ most recent elections, the socialists failed to defeat their counterparts on the right: Angela Merkel’s conservatives in Germany and Mark Rutte’s liberals in the Netherlands.

In both cases, an all-left government would have had to include parties from the far left, like Die Linke in Germany and the formerly Maoist Socialist Party in the Netherlands. To be seen working with them could have cost the mainstream socialists the support of moderate voters in the next election.

But the alternative — a grand coalition with their erstwhile rivals — has had a similar effect, disillusioning both parties’ more left-wing supporters.

Germany’s Social Democrats are polling around 25 percent after posting their worst election result in decades two years ago.

The Dutch Labor Party would get an all-time low of twelve out of 150 seats, according to the latest projections. The Socialists, at fifteen seats, could surpass it as the largest party on the left.

A grand coalition in Spain would probably do the same for the Socialists there. It would allow Podemos to claim that it is now the only credible left-wing alternative to pro-European and market-friendly rule. And it would all but guarantee another People’s Party victory in four years.