On April 28, Spain held parliamentary elections. But as yet, the parties haven’t agreed on a new government. This Monday and Tuesday, a fragmented parliament is set to debate and then vote on the candidate for prime minister, the incumbent Pedro Sánchez of the Socialist Party. So far, the candidate does not have the votes to win, although of course something could still change.

Do Spain’s political leaders have a cultural aversion to dealmaking? Not really. But since its return to democracy in the 1970s, Spain has not had a national coalition government. Political parties therefore lack experience in using the tools for building coalitions, such as sharing power. But Spain’s parties have built plenty of governing coalitions regionally and locally. What’s more, most of its national governments have governed in minority. All that requires striking deals.

So what’s the problem? Spain’s current difficulty in electing a new government has more to do with political polarization and the parties’ calculations about the governing formula that will best serve their interests. Let me explain.

What are the options for building a government?

The Congress of Deputies — the house that elects the prime minister — is highly fragmented. The center-left Socialist Party holds 35.1 percent of the seats, followed by the conservative Popular Party (18.9 percent), the center-right Citizens (16.3 percent), the radical left Podemos and allies (12 percent), and the far-right Vox (6.9 percent). Eight parties hold the rest, with the Catalan secessionist party, ERC, having the most.

After the elections, three government options appeared most likely: a Socialist Party minority government; a leftist minority coalition of the Socialists and Podemos; or a majority coalition of the Socialists and Citizens.

Why no coalition government of the Socialists and Citizens?

Despite being proximate on the left-right spectrum, a majority coalition between the Socialists and Citizens appeared unlikely from the start. This is in part because politics polarized on territorial and national identity issues. The April elections were the first since the 2017 push for independence in Catalonia. After years of political stalemate between Catalan independence leaders and Spain’s central government, run by the Popular Party, the Catalan parliament unsuccessfully declared independence in 2017. In response, Spanish authorities temporarily suspended Catalonia’s political autonomy and imprisoned independence leaders pending trial.

So while Spain’s parties differ on a left-right scale, they also break down by their positions on national identity and who should have what political authority across the territory. Catalan and Basque separatists occupy one end of this territorial scale. On the other are Citizens, the Popular Party and Vox. They stress Spanish nationalism.

Citizens and Podemos first entered parliament in 2015. Citizens started in Catalonia to oppose Catalan nationalism and stressed political renewal. Podemos also emphasized renewal. But its vision of Spain has room for multiple national identities and for a referendum on Catalan independence. Vox first entered parliament in 2019. It is staunchly conservative, anti-feminist and resolutely nationalistic. It wants to abolish regional governments, centralizing political authority in Madrid.

The Socialists supported suspending Catalonia’s autonomy. But the party claims to be willing to hold dialogue about Catalonia within constitutional boundaries. What’s more, Catalan and Basque secessionist parties supported the Socialist Party’s vote of no confidence against the Popular Party government of Mariano Rajoy, which brought the Socialists to power in 2018. The national parties of the right accuse Sánchez of cozying up to secessionists.

That different position on territorial issues is largely why Citizens ruled out negotiating with the Socialists. And there’s another reason: Citizens’ electoral support grew in the April elections, leaving it only a percentage point behind the Popular Party. Citizens’ belief that it might overtake the Popular Party as the main party on the right has made it reluctant to form a coalition with the Socialists, which would leave the Popular Party as the clear leader of the opposition.

Citizens’ boycott of the Socialists and the negotiation of regional coalitions with the Popular Party that rely on support from the far-right Vox have costs. High-profile figures have left the party. Yet the party leadership has held firm.

Could there be a Socialist government, with or without Podemos?

The other options also face stumbling blocks. The Socialist Party wants to govern alone. Podemos wants a Socialist-Podemos coalition government, which would nonetheless still be in minority.

Why would the Socialists prefer to govern alone, with only 35 percent of the seats? They may think that they can govern with less difficulty, if parliament would just agree.

Spain’s political institutions strengthen governments, once parliament agrees on them. A vote of no confidence — which would bring down the government — requires that an absolute majority of parliamentarians vote both to remove the government and simultaneously to select a new prime minister. Governments have strong powers to set the agenda, including the ability to issue executive decrees and carry over budgets into a new fiscal year, and tools to block unfriendly initiatives. Passing legislation often does not require an absolute majority (50 percent + 1); the government typically can pass a bill if it simply gets more yes than no votes.

Further, Socialists probably think that governing alone would give them more flexibility to forge ad hoc alliances to pass legislation. The party occupies the central policy position on both the left-right and territorial axes of political competition — based on data from the Chapel Hill Expert Survey. Theoretically, this means that the Socialists can form distinct majorities in parliament issue by issue.

Joining with Podemos in the government would pull the Socialists from the center and limit their alliance options on the right. That would also leave the government more reliant on secessionist parties.

Probably for these reasons, Podemos wants cabinet seats. Otherwise, it could be sidelined by the Socialists. Podemos performed poorly in spring elections and the party split. It may calculate that government posts will help assure its near-term survival. But the Socialists feel bolder, given their increased support in polls.

The Socialists have budged, a little. They progressively offered Podemos positions below the cabinet level, independent ministers proposed by Podemos, and later, Podemos ministers with a “technical” rather than political profile. So far, Podemos has held out for a coalition with its proportional share of political power.

Miscalculation could have high costs

This risk of miscalculation is high. The Socialists may overestimate their ability to forge diverse alliances if they govern alone. The territorial and left-right divides have hardened. And opposition parties’ electoral and governing ambitions may lead them to oppose the government’s policies, even if they view them as an improvement over the status quo. For its part, Podemos may underestimate the costs of governing. Cross-national research shows that voters punish junior coalition partners in the next election.

With or without the votes of Podemos, Sánchez needs the support or at least abstention of other parties to gain office. Failure would lead to a new attempt and/or repeat elections in the fall.

If there were new elections, citizens’ already substantial frustration with politics could grow, since it would be the fourth parliamentary election since 2015. If turnout declined, the right parties allied or the left fragmented, the left parties would likely lose seats that the right would gain.

Bonnie N. Field is a professor of global studies at Bentley University in Massachusetts and the author of “Why Minority Governments Work: Multilevel Territorial Politics in Spain” (Palgrave Macmillan, 2016).