Translate the following English sentence to French:
"What we must understand above all, however, is that, in the medium term, it is by producing a proactive immigration policy at European level, backed by clear criteria, which are shared by all Member States, that we will guarantee victory in this battle."
Mais il faut surtout comprendre qu'à moyen terme, le succès de cette bataille sera garanti par la formulation, au niveau européen, d'une politique d'immigration proactive, soutenue par des critères clairs, partagés par tous les États membres.