What Would Happen in the Senate if Vox Fields No Candidates: About 30 More Senators for the PP and the Reinforced Majority Within Reach

The conservative People's Party (PP) and the far-right Vox are negotiating for Vox to field no Senate candidates in all or some provinces. With today's forecast, if Vox withdraws everywhere and 80% of its voters vote for the PP's three candidates, the PP would go from about 109 to about 140 directly elected senators and would exceed the three-fifths reinforced majority of the chamber (161 of 267) in seven out of ten simulations, compared with 1% today. The main losers are the joint left-wing slate and the Socialists (PSOE), about 21 seats between them. But the effect depends on something that is not up for negotiation: that Vox voters, who will keep voting for Vox in Congress, mark the PP's candidates on the Senate ballot.

23 October 2026 · Miguel · Leer en español

What is being negotiated

The PP and Vox are negotiating a formula for the Senate. According to this week’s press, there are four options on the table: Vox fielding no candidates in the most contested provinces, Vox candidates running on the PP slate (the “2+1” formula), the PP giving Vox some of the senators chosen by the regional parliaments, or a package of political compensations (El Español; El Español). Reports mention between 12 and 19 provinces (ESdiario; El Español Aragón). As of today no agreement has been announced.

This article works out the simplest scenario: Vox fields no Senate candidates in any constituency and some of its voters vote for the PP’s. We show what changes, where, who wins and who loses, and what it depends on.

How the Senate is elected

Each mainland province elects 4 senators. Each voter can mark up to 3 candidates on the beige (“sepia”) ballot, and the 4 candidates with the most votes are elected, whatever their party (Article 166 of the electoral law). Because voters usually mark the three candidates of a single party, the usual result is 3+1: three senators for the most-voted slate and one for the second. Mallorca, Gran Canaria and Tenerife elect 3 (voters mark up to 2), Ceuta and Melilla 2 (up to 2), and the other islands 1.

This means the Senate rewards the winner heavily. If the PP and the left are tied in a province, the difference between winning and losing by one vote is two senators. That is why the votes that go to Vox today matter so much: they give Vox hardly any senators, but they can decide who comes first.

Today: where Vox wins senators

With today’s forecast, Vox wins an average of about 6.6 senators. It can only win them by finishing second, because it almost never finishes first in any province (at most 9% of simulations in Murcia and 13% in Ceuta).

Murcia (74%) and Almería (68%) are the only ones where it is more likely than not. Elsewhere, Vox competes for the fourth seat, the one that goes to the second slate.

If Vox withdraws

Today, the PP wins an average of 109 direct senators; the joint slate of the left and the PSOE, 82; Vox, 6.6. With the 58 senators chosen by the regional parliaments (23 of them PP), the PP reaches the three-fifths reinforced majority, 161 of 267, in only 1% of simulations; the absolute majority (134), in 51%; and the PP and Vox together, the absolute majority, in 75%.

If Vox does not run and 80% of its voters vote for the PP’s three candidates, the PP rises to about 140 direct senators, 31 more than today and 24 more than the PP and Vox together. The left falls to 61. In the full chamber, the PP would have only about 163 seats, above the three-fifths reinforced majority (161) in 71% of the simulations.

This is how the full chamber (267 senators, with the current regional senators) looks today and with a 50% and 80% transfer.

Absolute majority: 134. Three-fifths reinforced majority: 161.

How the simulations split among the four possible outcomes in the chamber, with the current regional senators.

It is worth distinguishing the two majorities. The absolute majority of the Senate is 134 senators, half plus one of 267, and is enough for most votes. The three-fifths reinforced majority is 161, and is required for decisions such as constitutional reform or the election of the Constitutional Court magistrates and of the members of the General Council of the Judiciary that the Senate appoints. With the reinforced majority, the PP would not depend on anyone even for those decisions.

Winners and losers

With an 80% transfer, compared with today:

• PP: about 31 more senators (from 109 to 140).
• Vox: loses its 6.6 direct senators. The negotiations talk of compensating this with regional senators, which do not change the bloc’s total. The PP has 23 today: even if it handed them all over, it would still have about 140 direct senators: above the absolute majority (134), but below the reinforced one (161), for which it would need Vox.
• Joint left-wing slate: 17.5 senators fewer, and the PSOE, where it runs alone, 3.8 fewer.
• ERC (Catalan pro-independence): 1.5 fewer; Junts (Catalan pro-independence) and EH Bildu (Basque left): 0.4 fewer each; PNV (Basque nationalists), Coalición Canaria and Soria ¡Ya! (a local party), around 0.1.

Where it is won and lost

Most of the effect is in the provinces where the PP and the left are currently fighting to finish first. With Vox’s votes, the PP would have the three seats of the most-voted slate almost assured.

• Comunitat Valenciana: in Valencia, the probability that the PP wins the majority goes from 17% to 84%; in Castellón, from 26% to 90%, and in Alicante, from 36% to 94%.
• Asturias (from 33% to 88%), Extremadura (Cáceres and Badajoz, from 43% to 92%), Navarra (from 41% to 77%) and Aragón (Huesca and Zaragoza, from around 50% to over 90%).
• One-seat islands: Lanzarote goes from 15% to 92%; Menorca, from 30% to 95%; Fuerteventura and Formentera, from 40% to 97%.
• Catalonia: the PP would win a seat it has no guarantee of today in Tarragona (from 0.3 to 1.8 senators on average), Lleida (from 0.2 to 1.4), Girona (from 0.1 to 1.0) and Barcelona (from 0.6 to 1.3).

And there are provinces where the withdrawal costs the right. In Murcia and Almería, Vox usually takes the fourth seat today as the runner-up. Without Vox, the PP already has its three, and the fourth goes to the left: the PP-and-Vox bloc loses an average of 0.6 senators in Murcia and 0.5 in Almería. In Ávila and Salamanca the same happens, to a lesser degree.

The effect is spread out. The 12 provinces where the right gains most add up to less than half of the total gain (46%), and the top 16, 57%. An agreement limited to a dozen provinces would capture, at most, half of the effect.

Split-ticket voting: what everything depends on

The calculation assumes that the Vox voter does two different things on the two ballots: votes for Vox on the white Congress ballot and marks the PP’s candidates on the beige Senate ballot. This is known as split-ticket voting, and it is not automatic.

• All three must be marked. In 4-seat provinces, the deciding senator is usually the PP’s third candidate against the left’s first. A Vox voter who marks only one PP candidate gives a vote to the first, who was going to be elected anyway, but not to the third, who is the one in play. For the decisive seat, what counts is how many mark all three.
• The reinforced majority depends on split-ticket voting. The PP would exceed the three-fifths reinforced majority (161) in 13% of simulations if only 30% of Vox’s vote reached its three candidates, in 34% with 50% and in 71% with 80%. (It would already have the absolute majority, 134, in 94% with 30%.)
• The Senate ballot is confusing. It is a long list of names on which each voter can mark up to three, from different parties if they wish. Without their party’s logo, some Vox voters may leave it blank, vote for a single candidate or make a mistake.

This is not voting advice: it describes the condition the scenario depends on. Without split-ticket voting, Vox’s withdrawal adds no seats to the PP: it only takes them from Vox.

What the calculation does not include

• No agreement has been announced. The scenario assumes withdrawal in every province; if it is partial, the effect will be smaller, and in Murcia or Almería, withdrawing costs seats.
• The 2+1 formula is not calculated here. If Vox’s candidates run on the PP slate, the result depends on how many PP voters also mark the Vox candidate, and vice versa. Our Senate model already calculates two variants, 2+1 slates in 16 provinces and Vox’s withdrawal in 19 with a transfer of between 55% and 85%, which we cover in our Senate analysis.
• The transfer is the same in every province. In reality it will vary, and it is likely to be higher where the Vox voter perceives that the seat is in play.
• No reaction from the left. Such an agreement could mobilize left-wing voters in the Senate, and that is not in the calculation.
• Senate voting is approximated with Congress voting. We use each province’s vote shares from the Congress forecast, corrected on the islands with the 2023 difference between the Senate and Congress, plus noise per candidate. We do not model the personal vote for specific candidates.
• Regional senators stay as they are today. Handing them to Vox does not change the bloc’s total, but it does change the PP’s reinforced majority on its own: every regional senator handed over is one fewer toward 161.

How we calculated it

• Forecast. The 50,000 simulations of today’s forecast, with the vote shares of each province and altnalysis’s Senate model: votes per candidate, bloc voting (the 4, 3, 2 or 1 most-voted candidates are elected) and the current regional senators.
• Scenario. In each simulation, Vox has no candidates and a fraction of 30, 50, 70, 80 or 90% of its vote goes to the PP’s candidates; the rest abstains. Same simulations and same randomness as today’s situation, so the differences are due only to the withdrawal.
• Left. The joint slate of the PSOE and Frente Amplio (left alliance, successor of Sumar) where it runs, and the PSOE and Sumar where they run separately.
• Code. articulo_senado_vox.py, in the altnalysis repository.