About Robert Mueller
Robert Mueller is a lawyer and a highly respected government official who served as the 6th Director of Federal Bureau of Investigation from 2001-2013. Previously Robert served as Marine Corps during the Vietnam War.

About the investigation in details
On May 17, 2017, Robert Mueller was appointed by Deputy Attorney General Rod Rosenstein as a Special Counsel to oversee an investigation into allegations of Russian interference in 2016 United States Presidential Election and related matters.
After the investigation through interviews, facts, and others by Robert himself and his team. Robert submitted the report to the Attorney General William Bar on March 22, 2019. And later to that, the Department of Justice released the special counsel’s final report on April 2018.
What happened in the testimony?
Robert Mueller stood in his testimony in front of Democrats and Republicans, and the house speaker was Nancy Pelosi. Mueller kept his statement precise, sometimes answering in one word and being pretty aware of the replications. And kept it around the 448-page report.
Robert said that President Trump was no exonerated by his report. His investigation did not exonerate Donald Trump’s obstruction of justice as claimed by the latter.
The Democrats tried every bit to take out something bog from Robert, by even questioning his team’s efforts. But Robert defended his team saying they did everything possible President Trump and his officials didn’t cooperate.

On Donald Trump’s interference
Instead of cooperating in the interviews and investigation, they interfered on many matters by trying to suspend and hush down matter. Trumps 2016 election agenda runner around the WikiLeaks which later was denied by the President.
Though the testimony didn’t generate any big headlines, many eyes were glued to it. President Trump himself said that his Post was in danger when he heard about the scheduled testimony.