Jews in the city of Córdoba allegedly "opened the doors" of the besieged city to the invading Moors. Whether this was an act of self-preservation by local Jews is anyone's guess, though I imagine people are using this fact as a justification for their own prejudice consistent with the idea (((they))) are behind mass Muslim immigration into Europe.
The Visigoths were decisively defeated at Battle of Guadalete in July 711 AD, which heralded the total collapse of Visigoth rule in Iberia. I'm not sure the loss of Córdoba really mattered in the grand scheme of things, even if Jews arranged for the fall of it. The Visigoth Kingdom was unstable and very quickly descended into chaos when it came under pressure from external forces.
The irony of course is Jews thrived under Muslim rule - both in Iberia and the Ottoman Empire.