What current scandal is testing the popularity of baseball as america's pastime?

Steroid use

Explanation:

There have been many scandals in baseball history.

The first one is the Black Sox 1919 World Series.

Currently, the composition of the balls are being very questioned, with questions that they may be juiced leading to very high home run rates compared to the history of the league. Normally, teams hit close to 0.8 or 0.9 home runs a game. After the 2015 All Star Game, in which there was lots of debate about how to increase scoring, with runs per game in the low 4's and lots of strikeouts, the composition of the ball changed, which lead to very high home run rates from the second half of the 2015 season on. For example, this year teams hit 1.40 home runs per game.

However, the scandar that tested the popularity of baseball as America's pastime was the Steroid Era, in the late 90's to early 2000's. After the 1994 lockout, fan interest declined. So, players started to use steroids, which the league didn't pay much attention, which led to individual Home Run records being broken. However, it was discovered that most of the best home run hitters of these years(Bonds, McGwire, Sosa) were on steroids, as were pitchers like Roger Clemens.