Levinsohn wrote in 1828:
'Our elders told us that some generations earlier the Jews in these parts spoke only this Russian language, and this Ashkenazi Jewish language we speak now had not yet spread among all the Jews living in these regions.'
https://en.wikipedia.org/wiki/Khazar_hypothesis_of_Ashkenazi_ancestry
Renan argued that conversion played a significant role in the formation of the Jewish people, stating that:
This conversion of the kingdom of the Khazars has a considerable importance regarding the origin of those Jews who dwell in the countries along the Danube and southern Russia. These regions enclose great masses of Jewish populations which have in all probability nothing or almost nothing that is anthropologically Jewish in them
https://en.wikipedia.org/wiki/Khazar_hypothesis_of_Ashkenazi_ancestry
In 2018, Elhaik stated that the Ashkenazi maternal line is European and that only 3% of Ashkenazi DNA shows links with the Eastern Mediterranean/Middle East, a 'minuscule' amount...
For Elhaik, the vehicle by which unique Asiatic variations on Ashkenazi Y-chromosomes occurred, with Haplogroup Q-L275,[103] was the Ashina ruling clan of the Göktürks, who converted to Judaism and established the Khazar empire.[104]
https://en.wikipedia.org/wiki/Khazar_hypothesis_of_Ashkenazi_ancestry