This is an updated version of an article published in June that explains what we know about obstruction of justice and how it relates to President Trump’s actions.

President Trump’s assertion that he fired his former national security adviser, Michael T. Flynn, in part because he knew that Mr. Flynn had lied to the F.B.I. about his conversations with the Russian ambassador — for which Mr. Flynn pleaded guilty on Friday — has intensified accusations that the president committed obstruction of justice.

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While it can be a murky task in court to interpret the obstruction statutes, said David Sklansky, a former federal prosecutor who teaches at Stanford, impeachment proceedings are different. They are a “quasi-judicial, quasi-political process,” he noted; the House and the Senate determine for themselves whether the standards are met.