WASHINGTON — When Jeff Sessions appeared before the Judiciary Committee early in January, his confirmation as attorney general was not in doubt.

Senate Republicans enthusiastically supported the nomination of Mr. Sessions, a longtime friend and colleague from his two decades as a Republican senator from Alabama. Democrats on the committee, facing a man many of them had served and supped with, tempered their push on Mr. Sessions’s troublesome history on civil rights, and he seemed to escape their questioning relatively unscathed.

Mr. Sessions should expect no such senatorial courtesy when he appears at a hearing of the Intelligence Committee on Tuesday. Democrats believe that Mr. Sessions repaid their earlier hospitality by lying to them — and the Senate — about his contacts with Russian officials, and they are now determined to extract clear answers.

“Jeff Sessions has already demonstrated a willingness to mislead the Congress,” said Senator Ron Wyden, Democrat of Oregon and a member of the intelligence panel. “There are a lot of important issues to get into.”

How the Senate should treat one of its own is always complicated. While they may often disagree on fundamental matters, senators spend time together on the floor, in the gym and at countless hearings, and they often develop amiable and respectful relationships over the many years they coexist. Being a member of the club is usually thought to entitle a senator to a degree of deference when it comes to confirmation for a high-level administration post or an appearance before the Senate in one capacity or another. Consider that Hillary Clinton was confirmed for secretary of state in 2009 on a vote of 94-2.

But having served in the Senate is not always a guarantee. The most famous example was John Tower, the conservative Texas senator who was rejected as President George Bush’s nominee for defense secretary in 1989 after former colleagues deemed him unfit for the job because of character issues and potential business conflicts. Former senators have had a tough go in more recent years as well. Chuck Hagel, a former Republican senator from Nebraska, took a beating from his former side of the aisle when he was nominated as defense secretary by Barack Obama in 2013, though he survived to…