What happens if a newly chosen senator gets thrown into the middle of an impeachment trial?

Ask Sen. Chris Coons.

“Oddly enough, I was in exactly that fact pattern,” the Delaware Democrat said in a recent interview. “Mine was a special election in 2010. I was seated right after the election.”

To be sure, it was not a presidential impeachment that autumn, but Coons still found himself arriving in the Senate under rather unusual circumstances.

The House voted unanimously to adopt four articles of impeachment against U.S. District Judge G. Thomas Porteous Jr. in March 2010. In that case, the Senate opted to impanel an Impeachment Trial Committee of a dozen senators to hear the evidence and produce a report for the whole Senate.

Among the members of the Porteous committee was Delaware Democrat Ted Kaufman, who was appointed interim senator after his longtime boss Joe Biden became vice president in 2009.

“My predecessor had sat through a lot of the early stages of it, and so in order to be able to participate in the deliberations of the Senate, I needed to be brought up to speed on a lot of the background,” Coons said. “Sen. Kaufman had been part of … the stages of the impeachment process before it got to the floor, and I remember getting just enormous briefing binders, and having to read up on a lot of background material.”

Porteous was ultimately found guilty by the Senate and removed from office, and the votes were not close, but the circumstances do provide some of the most recent precedents.

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Coons took the Senate oath of office before Illinois Republican Mark S. Kirk, who had won the special election to fill the unexpired term vacated by senator-turned-president Barack Obama, but Kirk, a former congressman, actually recused himself from the impeachment trial.

That’s because he had voted in favor of the articles of impeachment in the House, and declared himself to thus have a conflict of interest that prevented his service on the Senate jury.

There’s at least a chance that something similar might happen this year, with even greater stakes.

Georgia Republican Sen. Johnny Isakson has already already announced he will resign at the end of the year, as he continues to deal with Parkinson’s disease and other health issues.

Georgia law will allow GOP Gov. Brian Kemp to appoint a replacement, but there is a possibility Isakson and his successor might reach different conclusions on whether to convict President Donald Trump and remove him from office.

As unlikely as that may be, the new senator would most probably get to be a full participant, even if he or she were sworn in after the House has presented articles of impeachment to the Senate. House Judiciary ranking member Doug Collins is one of the candidates seeking the appointment by the Georgia governor.

The great historical example dates back to the 1868 Senate impeachment trial for President Andrew Johnson.

Maryland had a vacant Senate seat because the chamber had refused to seat former Gov. Philip F. Thomas, alleging he had taken up arms against the Union during the Civil War.

Less than 24 hours after Chief Justice Salmon Chase convened the Senate as a court of impeachment in March 1868, a committee of Maryland state legislators arrived at George Vickers’ home on the Eastern Shore to bring him on a journey to Baltimore on an ice boat and on to Washington by train, according to the Historical Society of Kent County.

Vickers would be sworn in on March 7, allowing him time to take the oath of office and be sworn in as part of the impeachment proceedings.

Any pending impeachment proceedings likely could be interrupted temporarily to swear in a new senator, should the need arise.

While there may be no exact precedent, people familiar with the Senate’s deliberations say there would be nothing to preclude the participation of the appointed Georgia senator, assuming he or she has taken  both the Senate oath and the second oath administered as part of an impeachment trial.