Facebook's chief legal adviser Colin Stretch responded to the Senator John Thune’s accusations of political bias. He posted a relevant statement on the Facebook blog. 

The statement says that the company has investigated the work of the news section and writes its conclusions to the Senator.

"Our investigation has revealed no evidence of systematic political bias in the selection or prominence of stories included in the Trending Topics feature,” said the lawyer.

According to him, conservative and liberal topics have been covered at almost equal pace.

"At the same time, our investigation could not fully exclude the possibility of isolated improper actions or unintentional bias in the implementation of our guidelines or policies,” said Stretch.