When U.S. Sen. Jon Tester was elected last November from Montana, he famously became the most junior senator in the country, ranked dead last in seniority in the 100-member Senate.

Tester moved up to 99th this summer after the death of Wyoming’s Republican Sen. Craig Thomas.

Now, in the wake of the sex scandal involving Idaho Sen. Larry Craig, Tester could be moving up the seniority ladder again.

Craig, a Republican, pleaded guilty earlier this month to disorderly conduct after he was arrested in an undercover sting to catch people soliciting sex in public restrooms in the Minneapolis airport. Key Republicans are asking the three-term senator to resign.

As of press time Thursday, Craig had not yet said if he would vacate his seat.

A Craig resignation would place Tester, a Democrat, at 98th on the seniority list.

Not that it matters a whole lot to Tester, said Don Ritchie, the associate historian in the U.S. Senate. Going from 99th place to 98th won’t mean Tester gets a bigger office, better committee assignments or the opportunity to move his desk from the very back of the Senate floor.

“It’s more symbolic to move from 100th to 98th, but before long he’ll be 88th, then 68th,” Ritchie said. “Everything in the U.S. Senate operates on seniority.”

Craig’s resignation — should it come — wouldn’t affect Sen. Max Baucus, Ritchie said, because Baucus already outranks Craig. Baucus is 9th most senior member of the Senate and has already earned a big office and good seat.

Neither would Craig’s potential resignation change Tester’s spot on committees. Craig and Tester both serve on the Veterans Affairs Committee. But committee seniority is assigned by party, Ritchie said. That means other Republicans on the committee might move up a slot if Craig resigns, but Democrat Tester will stay right where he is.

Seniority in the Senate is based on a number of factors, Ritchie said. Most obviously, it’s based on how long someone has served in the Senate. If several new senators are elected at once, as Tester and others were, seniority is set by a series of complicated rules, including whether the senator previously served in the House, as governor or in other offices in his or her respective state.

Seniority even can come down to when the senator’s state became a state, Ritchie said.

Seniority cannot be inherited, which is why Craig’s replacement, should the senator resign, would start at the back of pack — where Tester once was.

Tester’s office had no comment for this story.