Mariano Rajoy will on Wednesday become Spain's first sitting prime minister to be called to court as he appears as a witness in a long-running graft trial that has rocked his conservative party and hurt him at the ballot box.
Rajoy returned to power for a second term last October with a severely diminished mandate, after a series of corruption scandals tainted several members of his People's Party (PP) and turned off voters.
The prime minister's court appearance turns the spotlight back on one of the most prominent cases at a delicate time for Rajoy, who no longer enjoys a majority in parliament and has to scrape together votes to get laws through.
He had sought to testify by videoconference, arguing that the journey to the court of San Fernando de Henares on the outskirts of Madrid would be a waste of taxpayer money. But the request was denied by Spain's High Court.
The trial follows a long graft investigation into several city councils which are alleged to have received illegal financing from a network of companies.
Known in Spanish as the "Gurtel" case, after the nickname of supposed mastermind and businessman Francisco Correa, the probe ended up reaching several former high-ranking PP members and drew attention to an alleged party slush fund.
Former PP party treasurer, Luis Barcenas, is among those on trial on charges of organized crime, falsifying accounts, influence-peddling and tax crimes.
Rajoy is expected to be grilled about the alleged slush fund and his knowledge of party business in the early 2000s, when he held several senior positions in the PP.
He has previously denied receiving any illegal funds.
The prime minister has sought to distance himself over the years from this probe and other corruption scandals, but his turn as a witness is likely to be seized upon by opposition parties who have repeatedly called for him to step down.
That is unlikely to have any immediate consequences - left-wing parties including the Socialists and Podemos ("We Can") have failed in their bids to oust Rajoy before, as they lack the clout in parliament and are divided on many fronts.
But it could still be damaging for the prime minister and his party.
"Corruption issues will continue to put a ceiling on the PP's electoral aspirations," Antonio Barroso, deputy director of research at Teneo Intelligence said in a note. "While Rajoy should be benefiting from [Spain's] strong economic rebound, the ruling party has been losing support in the polls recently."