What happened in Spain is that they joined the Euro currency, and this caused a massive boom from 2001-2007 where GDP more than doubled in only 6 years. This was mostly fueled by capital transfers from other Eurozone countries, seeking higher returns than in their home country.

Of course this rate of growth proved unsustainable: in 2008 the (Spanish) real estate bubble burst and this caused bank bail outs, massive unemployment (rates around 25%), and put an end to GDP growth for many years, exacerbated by the fact that Spain did no longer have its own currency to devalue in order to regain international competitiveness.

At the time the bubble burst, government debt in Spain was at a bit more than 40% GDP, with a budget surplus, far lower than for example the "responsible" Germany at more than 60%.

Now what does any of that have to do with "socialists"? If anything, it's a cautionary tale about badly designed currency zones and financial markets misallocating capital.