Are candidates debating less than they used to?

All eyes are on Pennsylvania as the two nominees for U.S. Senate — Republican Dr. Mehmet Oz and Democrat John Fetterman — prepare to square off in their first and only debate Tuesday.

The phrase “first and only” has become an increasingly common descriptor of this year’s debates and there’s evidence to suggest the traditional format — wherein candidates stand on a stage and exchange ideas — may be a thing of the past.

As recently as 2010, there were 17 debates across the five most competitive Senate races, according to...