Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: (CNN) Justice Department special counsel Robert Mueller's one-two punch on Monday sent a forceful message to President Donald Trump, the public and potential suspects about the case he is constructing of Trump associates' involvement with Russia during the 2016 campaign. Mueller showed he can keep a secret and maximize the impact of what he makes public. In the first major filings of his investigation into the Russian effort to influence the election, Mueller revealed how broadly he has taken his mandate, the kinds of records he has uncovered, and how he has leveraged at least one insider to cooperate.Robert Mueller showed he can keep a secret and send a powerful message to WashingtonHe has taken his mandate as special counsel broadly and leveraged at least one insider to cooperate 
 Question:It had contained information about his communications with _ nationals.

Russia