During Spain’s XV Legislature, the Senate became one of the country’s principal arenas of political confrontation. The Partido Popular (PP), with 142 senators and an absolute majority, used its control of the upper chamber to investigate the government and challenge its legislative agenda, while the PSOE and its allies held the governing majority in the Congress of Deputies. The imbalance turned the Senate into a counterweight to Pedro Sánchez’s coalition, expanding its role beyond territorial representation and second reading.
The PP promoted seven investigative commissions during the legislature, covering the Koldo affair, the Centre for Sociological Research (CIS), the state holding company SEPI, the Adamuz railway accident, RTVE, the April 2025 blackout and the DANA disaster. The Senate’s Koldo inquiry examined government and public-sector contracts, licences, concessions, subsidies and other operations connected with Koldo García Izaguirre and people linked to the Operación Delorme investigation. The commissions could summon witnesses, who were required to tell the truth, and brought senior Socialist figures and government officials before the chamber. The PP also registered an eighth commission concerning alleged irregular mass immigration into Ceuta, but it did not become operational before the legislature ended.
Pedro Sánchez appeared before the Koldo commission, placing the prime minister before an inquiry established by the opposition-majority chamber. Sánchez dismissed the proceeding as a “circus.” The commission also summoned former transport minister José Luis Ábalos, Koldo García and former prime minister José Luis Rodríguez Zapatero. Its remit focused on public-sector dealings associated with the wider Operación Delorme investigation.
The PP’s influence extended to the Senate’s legislative procedures. In 2023, the party used its majority to amend the chamber’s rules, giving the Senate’s governing board, the Mesa, greater scope to extend the time available to consider bills sent by Congress. The change was used in the handling of legislation including the amnesty law, delaying its progress through the upper chamber. In March 2025, Spain’s Constitutional Court struck down the rule change. The dispute formed part of a wider institutional clash: reporting during the legislature recorded as many as seven conflicts of attribution raised by the Senate against the government.
The Senate’s authority has practical constitutional significance as well as political weight. Certain procedures, including authorization under Article 155 of the Spanish Constitution, require an absolute majority in the chamber. In ordinary legislation, but, Congress remains decisive: the Senate can amend or delay bills, but the lower house has the final say under the constitutional process. That division helps explain why the PP could use its Senate majority to scrutinize the government and slow legislation without controlling the government’s agenda in Congress.
The PP also advanced 41 Senate bills, collectively dubbed the “leyes Feijóo,” including proposals concerning public tributes to former ETA members, the protection of official symbols and rules governing utility cut-offs in cases involving squatters. The article’s account describes these measures as stalled in Congress, where the PSOE and Sumar controlled the agenda. The resulting divide between the chambers made legislative confrontation a defining feature of the period: the Senate could advance opposition initiatives, while Congress determined whether they would proceed.
Political tensions were also visible in the chamber’s day-to-day proceedings. Cameras captured PP spokesperson Javier Arenas vaping during a plenary session, while heated exchanges prompted disciplinary warnings from Senate president Pedro Rollán. The Senate’s expanded role drew heightened media attention as it became a venue for high-profile inquiries and clashes between the opposition and the government.
The split in political control had a precedent in 2018, when Sánchez became prime minister while the PP held a Senate majority, but that arrangement was brief. During the XV Legislature, the PP’s 142 seats gave it a sustained absolute majority, while the governing bloc retained control of Congress. The result was a prolonged institutional standoff, with the Senate functioning as a political counterweight and Congress remaining the decisive chamber for the government’s legislative programme.
