1. The special counsel Robert Mueller was a reluctant witness during two hearings on Capitol Hill.

Republicans sought to undermine him and his investigation, and Democrats to highlight his most damning findings.

Mr. Mueller defended his work and sought to drive home to lawmakers and the public the grave implications of his report, particularly on the systematic effort Russia made to influence the 2016 presidential election.

But he also left a great deal unsaid. Sometimes appearing confused or at a loss for words over hours of testimony, he declined repeatedly to offer his opinion on key questions, including impeachment, or even to read directly from the 448-page document.