A long-time U.S. senator, Patrick Leahy of Vermont, is now third in the line of presidential succession in the country.

Leahy, a Democrat who has served in the Senate since 1975, was sworn in Tuesday as the president pro tempore in the upper chamber of Congress. It is a largely ceremonial position he is assuming after the death Monday of Hawaii Senator Daniel Inouye.

But the position, by law, also puts the 72-year-old Leahy third in line to the U.S. presidency, behind Vice President Joe Biden, another Democrat, and House Speaker John Boehner, a Republican.

In the U.S., no one below vice president has assumed the presidency upon the death or resignation of the president.