So how do McAllister and Radel stack up with other short-timers? Well, it's complicated.
The Office of the Historian of the House of Representatives doesn't keep a tally of the shortest-serving members, because there are several variables, including instances when someone was elected to a House seat but died or resigned before taking office.
This much we know: Historians generally agree that Effingham Lawrence is the shortest-serving lawmaker ever. He served as a Democratic representative for just one day – March 3, 1875 – on the last day of the 43rd session of Congress.
Recent reports by the nonpartisan Congressional Research Service gives us a general sense of lengths of tenure.
At the start of the current Congress, the average years of service ran 9.1 years, according to CRS. During the 20th century, the average years of service for House members steadily increased a little more than four years to approximately a decade in the three most recent congressional sessions.
And as the chart below shows, the percentage of House lawmakers who decide not to seek reelection has steadily dropped through the years. In other words, being a lawmaker has become more and more of a career than a temporary profession:
Things are a little easier to track in the upper chamber, where the historian's office has kept this nifty list of short-time senators for years. Notice that several have served just in the past years after a series of deaths, resignations and campaigns for higher office led to a series of vacancies: