I don't know how old you are, but the last time there was a serious challenge to an incumbent was 1976 with Gerald Ford and Reagan. Although, in 1980, Carter was challenged by Ted Kennedy, and that was more serious as it was the last incumbent who lost a primary in any state until this year in American Samoa. There were some other challengers in other incumbent primaries, but none were as serious as 76 and 80. 1972, there basically weren't any, Nixon had an iron grip on the party. Of course, in 1968, LBJ chose not to seek reelection, so it isn't applicable. 1964, there wasn't a primary in every state, but the challenger was a George Wallace, and it was more successful, but only because it was George Wallace and the party switch was just starting. 1956 had one real challenger, but Eisenhower won 85.9% of the vote overall, so it wasn't serious. 1952 was probably the most robust of the older elections, Truman lost the New Hampshire primary and decided not to run for a "third" term. 1948 had a more serious challenge, but it wasn't in every state, and Truman overall got 64.7% of the vote. 1944 again didn't have that serious of a challenge with FDR getting 79.3% of the vote. 1940 had a bit more serious of challengers, but FDR still got 71.93% of the vote. 1936 barely had anything, and FDR, similar to Obama in 2012, got 92.9% of the vote. 1932 had a much more robust challenge with Hoover since it was the great depression but that was a completely different situation. And Hoover actually got 36% of the vote. But he had control of the party, and the convention went with him.

More modern wise, 1984 was basically nothing. 1992 was a bit more serious, but Bush overall got 72.8% of the vote, and Buchanan got 23%, but Bush didn't lose a race. 1996 saw Clinton get 89% of the vote, he technically lost two races. One in north Dakota, but it was a different race cause that person won with 651 votes total. The second was to uncommitted in Michigan. And not every state held a primary. And finally, in 2004, Bush got 98.1% of the vote, so again, it was not a real challenge.

Again, I don't know how old you are, but I think all this shows that it's super rare for an incumbent to have any robust challenge in modern history. With mainly 76 and 80 being the main ones. Even the older ones where the incumbent lost races weren't usually that robust. And debates were even rarer with only really happening in 76. So overall, this year was pretty standard for incumbent challengers.

Sources: 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1964, 1968, 1972, 1976, 1980, 1984, 1992, 1996, 2004

Sidenote here at the end. I did this all on mobile, and it took way too long, but I didn't want to just give up.