Sally Yates was the acting Attorney General during the Trump transition. She appeared before a Senate committee that was ostensibly investigating Russian efforts to influence the presidential election. Republican senators were more interested in how information about Flynn was leaked to the Washington Post. They also wanted to know why she refused to defend Trump's travel ban. One Republican senator even changed to subject to Hillary Clinton's use of her private email server. The Republicans seemed uninterested in getting to the real issues about Russia's efforts to influence the election and how to prevent it from happening again. Above all, the Republicans want to contain the damage done to the Trump administration to Flynn's mistake. They don't want to know about other connections between the Trump campaign and Russia.
Yates did provide some new information about Flynn. She met with the White House attorney and told him that Flynn was compromised when his discussions about government sanctions with the Russian ambassador was made public. That made him subject to Russian blackmail. Someone in Flynn's position should not be vulnerable to blackmail or other forms of influence. Flynn remained in his top secret position for 18 days before he was removed from office.
Yates answered questions from Republicans about her refusal to defend Trump's travel ban very clearly. She said that it was unlawful and in violation of the Constitution. It was unlawful because Trump had made his intentions about a Muslim travel ban known by numerous statements he had made during his campaign. She rejected Trump's claim that the ban was only about national security. She also pointed out that several federal courts had made a similar conclusion about Trump's travel ban.
It seems pretty clear that Republicans do not want to dig deeply into the connections between the Trump campaign and Russia efforts to influence the election. They are more interested in defending Trump by deflecting attention to other issues. That defense will work unless the investigation is turned over to an independent prosecutor.