The brother-in-law, or cuñado, holds a prominent, yet unenviable, position in Spanish society, transcending the realms of the family tree to become something more than just a relative. He’s a symbol, a social phenomenon, a state of mind.

The exact characteristics of the archetypal cuñado are up for debate, but they tend to be negative. He is an extroverted, matey, slightly boorish, know-it-all who greets you effusively but doesn’t really listen to what you have to say. On the contrary, he loudly broadcasts his own opinions, often political, over Christmas dinner.

“For the brother-in-law, everything is communism, everything is Venezuela, everything is Eta,” Lorena G. Maldonado, of El Español newspaper, has written. “In his holiday photo album he’s pretending to hold up the Tower of Pisa, he’s first in line when there’s a conga at a wedding, he stirs the Sunday paella and smiles as he says: ‘I’m Spanish, what do you want me to beat you at?’ He saw the property bubble coming a long way off, he was there, he already knew, he told you so…”

For many (Maldonado included), Spain’s highest-profile cuñado is Albert Rivera. That’s in great part because in 2016, Podemos leader Pablo Iglesias, in one of those finely calculated moves that he specialises in, cast the leader of Ciudadanos as such during a parliamentary debate. The slightly comic accusation was based on Iglesias’s claim that Rivera’s ideology derived from the same family as the right-wing Popular Party (PP). But there was also a hint of the more personal use of the term – the smug paella-stirrer – which has since stuck to Rivera like rice to a pan.

In some ways he does indeed fit the cuñado stereotype, if only in terms of aesthetics and style. There is the clean-cut-but-casual attire, the bumptious self-confidence, the apparent knowledge about any subject and ready response to every problem, which can both impress and grate. But even his critics now have to take Spain’s most popular national party leader seriously.

In recent months, Ciudadanos has been riding high in voter intention polls, even proving to be the most popular party in Spain, according to Metroscopia. Rivera, meanwhile, is regarded less and less as a mere opposition upstart who bangs on about corruption and Catalonia and more and more as a potential prime minister.

But while that possibility becomes increasingly feasible, the place Ciudadanos occupies on the political spectrum has remained somewhat fuzzy.

The brother-in-law, Maldonado explains, with a large dose of irony, “is neither on the left or the right; instead he’s straight up, salt-of-the-earth, genuine.” What Maldonado means is: that’s how he presents himself, although after a few glasses of La Rioja he’ll start on about communism and Eta.

Rivera, meanwhile, in a very cuñado-esque bit of rhetoric, told The Economist recently: “We have to move away from the old left-right axis”. Not so long ago, his party was describing itself as “centre-left”, its business-friendliness offset by mostly liberal social policies. But almost exactly a year ago, Ciudadanos redefined its ideology, removing “social democracy” from its statutes, leaving a definition of it as “constitutionalist, liberal, democratic and progressive”, which does little to clarify the issue (after all, who would suggest that being “unconstitutional, illiberal, undemocratic and regressive” was a good idea?). A dig into the archives further muddies matters, with Rivera flip-flopping on gay marriage, opposing abortion as a right, showing an ambivalent take on historical memory, announcing a refusal to support Rajoy as head of a new government in 2015, forming a putative governing pact with the Socialists in 2016, then supporting a new PP government (with Rajoy at its head) a few months later.

Confused? Understandably so. But then again, Spanish politics is a weird, many-mirrored place at the moment and similar charges of inconsistency could also be levelled at the Socialists or the Catalan secessionists.

But recent events in Catalonia, where Rivera’s party has been hogging the unionist limelight, have, finally, appeared to nail it down as a party of the right. With Rajoy’s PP still mired in a smorgasboard of corruption scandals and having failed to solve the territorial crisis, Ciudadanos has benefitted, winning the Catalan election under the candidacy of Inés Arrimadas and cheerfully surfing the wave of Spanish neo-nationalism. To put it crassly, the Catalan crisis has been kind to Ciudadanos.

Conspiracy-prone supporters of independence regularly claim Ciudadanos are right-wing extremists and rabid independentistas tend to portray them as fascist, a term that has lost its currency in this age of the easy insult and which really isn’t relevant in this debate. (One thuggish wag painted “Neo-fachas” on the doorstep of the party in L’Hospitalet de Llobregat recently; one twitter user accused me of receiving funding from Ciudadanos the other day for suggesting in an article that the party was moving away from the PP on the historical memory issue).

But no, they are not the crypto-Francoist, goose-stepping loonies their enemies desperately try to portray them as.

Yet it does seem that Ciudadanos finds itself in a rum, rather disturbing, position – let’s call it Rivera’s Conundrum.

Created as a nationwide force in 2014 with the promise of introducing a centrist, transition-style statesmanship to Spain’s tribal politics, in Catalonia the party has become precisely the opposite, doing as much as any other to rattle the cage of tribalism. The more polarised the territorial crisis has become, the more Ciudadanos has hoovered up anti-independence votes. And it has heartily contributed to that polarisation, positioning itself as yin to Carles Puigdemont’s exiled yang, with the PP often a hapless bystander.

One of my favourite cartoons of recent months was a picture of Rivera marching along, bashing a drum marked “Article 155” – the clause in the constitution allowing Madrid to implement direct rule. His insistence throughout much of last year that this drastic measure be introduced often left Rajoy looking timid and, dare I say it, moderate, in comparison.

Ciudadanos’s approach to this issue was on display recently in Madrid during a BBC World Questions debate, panelled by representatives of Ciudadanos, the PP, the Catalan Republican Left (ERC) and journalist Ana Romero. The most belligerent voice in the room was not that of the PP’s Francisco Martínez or ERC’s Alfred Bosch. It was Begoña Villacis, of Ciudadanos, whose insistence on attacking the Catalan independence movement at every turn – even, bizarrely, when the debate had moved on to Gibraltar – which gave the event a slightly sour aftertaste.

And there are signs that, in its determination to keep stealing voters from the PP, Ciudadanos’s hard-line playing to the gallery is seeping out of Catalonia, into its national politics (see its attempts to remove the Basque government’s historic right to controlling its own taxes, or its U-turn on the issue of life imprisonment).

So where does this leave Spain’s best-known brother-in-law? After years of shifting around, and with the corridors of power apparently beckoning, it’s time he made clear where exactly on the political right he and his party stand as a government-in-waiting.

Worryingly, Rivera’s Conundrum dictates that if he shows any willingness to step back, to make concessions – to stop banging the drum – he’ll lose votes. Given that Puigdemont’s Conundrum dictates similar terms for the ousted Catalan president, don’t expect to see much bridge-building any time soon.