I took a look at the Dodgers at the start of the season when they broke from the pack with a 12-2 record. I found that the average final year winning percentage for all teams that start at 12-2 or better was .585 or 95-67 for a 162-game record.
Well, since then the Dodgers have gone 44-66 and now own a 56-68/.452 record, which is good for third place in the NL West, 5 games back in the retrograde division. They are in tenth in the wild card hunt, 10.5 games behind the Astros. Their only bet for a postseason berth is the division title, but they can't expect the division leader to remain under .500 as they switch to intra-divisional games down the stretch.
Basically, they had better win some games, which has been hard for them to do for quite some time. They have not had a winning record since they finished getting swept by the lowly Royals and fell to 33-32 on June 16. Up to that point, they had spent one day (opening day) under .500 all year. Since then they have had one daythe next day when they fell to the ChiSox, 6-0, to start another sweepat .500 or better. Since the start of that Royal series, Dem Bums haz gone 23-39 (.371).
But how bad is that? Is that the worst that a once 12-2 team finished. Well, no, but it's close. The 1914 Pirates started 12-2 and finished with a slightly lower winning percentage (by 4 points), but the Dodgers can still topple (bottom-le) them.
The 1914 Bucs were actually 21-8 at one May 25. At that point the eventual league champs, the "Miracle" Braves, were 8-19, 12 games back. The Pirates then lost ten games and 15 of 17, at which point they fell to a .500 (23-23) record. From that point forward, they had three days with a winning record. It didn't help that they went 5-17 against the "Miracles"'s and 6-16 against the fifth-place Robins (soon to be Dodgers).
The Pirates are the only one of the 12-2 or better teams to finish more than one standard deviation away from the mean winning percentage (STDDEV is .062). The Dodgers are currently over two standard deviations away from the average.
It can be said that the degree to which the Dodgers reeked after their fast start is quite rare. Here are the final results for all 12-2 or better teams arranged by winning percentage in ascending order: