From the study’s conclusion:
Our findings extend previous research that shows that efforts by mainstream parties to attract voters by adopting far-right issues tend to strengthen far-right parties (Abou-Chadi Reference Abou-Chadi2016; Abou-Chadi and Krause Reference Abou-Chadi and Krause2020; Bale Reference Bale2008; Meguid Reference Meguid2005). The findings suggest that the political communication by mainstream parties plays a central role in the electoral success of the far right. Moreover, far-right agenda setting in public debates not only influences electoral fortunes but also has broader implications for democratic discourse: it contributes to the discursive mainstreaming of far-right ideas.
I guess it’s good there is proof for it. Too bad this is what has been obvious for like… what, going on a decade now? And no-one is abandoning the strategy.