WASHINGTON (Reuters) - When Robert Mueller finally appeared in public on Wednesday to defend his investigation of President Donald Trump, he often struggled with questions and, hours into a long session with U.S. lawmakers, had to correct one of his own answers.

Former Special Counsel Robert Mueller stands before the House Judiciary Committee as he prepares to testify at a hearing on the Office of Special Counsel's investigation into Russian Interference in the 2016 Presidential Election" on Capitol Hill in Washington, U.S., July 24, 2019. REUTERS/Jonathan Ernst

The silent force behind a sweeping investigation that has loomed over nearly all of Trump’s presidency, Mueller, 74, was praised by lawmakers from both parties for his decades of service as a soldier and a federal attorney.

But he faltered in some of his replies and he refused to respond at all to many of the rapid-fire questions, as he mainly limited his responses to the text of the report he submitted to the Justice Department in March.

Mueller’s testimony came during back-to-back hearings before the House of Representatives Judiciary and Intelligence committees.

David Axelrod, who served in Democratic President Barack Obama’s White House and was chief political strategist for Obama’s presidential campaigns, said in a tweet that Mueller “clearly was struggling today and that was painful.”

At the start of the Intelligence panel hearing, Mueller said he wanted to correct a statement from earlier in the day.

In reply to a question from Democratic Representative Ted Lieu in the Judiciary hearing, Mueller had indicated that he did not prosecute the president for obstruction of justice because of a Justice Department policy preventing him from doing so.

Hours later, Mueller said he wanted to correct that exchange with Lieu. He said, “We did not reach a determination as to whether the president committed a crime.”

Republican members of both panels took a confrontational tone with Mueller. Republican Representative Brad Wenstrup asked Mueller after posing a question, “Are you following that?”

Mueller repeatedly asked lawmakers to repeat their questions, which were typically rushed because each member of both committees was limited to five minutes for questioning him.

Mueller, in turn, kept his answers short and repeatedly referred questioners to his 448-page report, made public in mid-April, summarizing his 22-month investigation of Trump and Russian meddling to aid him in the 2016 U.S. election.

“Where are you reading from?” Mueller asked at one point during Judiciary’s question-and-answer session.

“I am reading from my question,” Republican Representative James Sensenbrenner said.

When Democratic Representative Zoe Lofgren asked him who the Russian government preferred to win the U.S. presidency, Mueller responded: “Well, it would be Trimp - Trump.”

Mueller, a former director of the FBI, displayed little emotion. But, when asked if he was no longer special counsel, a smile crossed his face.