The Washington Nationals' bullpen spent the first couple months of the season coughing up leads in games. Recently, they've graduated to coughing up the division lead.
In the space of one week (June 6–12), the first-place Nats lost four games off their division lead, going from a season-high 12.5 games ahead in the NL East to just 8.5 games up. Granted, there are 28 other teams in the league that would kill to have "just" an 8.5 game lead (the Astros are all set, thanks). Still, when you lose a third of your cushion in the blink of an eye, it’s concerning.