Republican John Kyl of Arizona, who served three terms in the Senate before retiring in 2012, has been sworn in to fill the seat left open by the death of Sen. John McCain.
Kyl has only committed to serve until the end of the current congressional session on Jan. 3. Still, he'll have the chance to cast key votes, including whether to confirm Brett Kavanaugh to serve on the U.S. Supreme Court.
His support will give Republicans more cushion to confirm Kavanaugh before the midterm elections in November.
Senate Majority Leader Mitch McConnell says he could not be happier that the "new, not-so-junior senator" will be working during a time that he described as "all hands of deck for the American people."
Vice President Mike Pence swore Kyl in.