Backtracking Bernie Sanders Takes Off the Gloves

It wasn't that long ago that Bernie was condemning Donald Trump for attacking Bill Clinton for his alleged sexual indiscretions as evidenced in the following news article dates 1-3-16:

Democratic presidential candidate Bernie Sanders slammed Republican front-runner Donald Trump for his attacks on Bill Clinton. "We have more things to worry about than Bill Clinton’s sexual life,” Sanders said Sunday on ABC’s “This Week.”
[link to abcnews.go.com]

Fast forward to 1-8-16 when Bernie performed the Fosbury Flop:

Democratic presidential candidate Bernie Sanders called Bill Clinton’s sexual indiscretions during his presidency “totally disgraceful and unacceptable,” while campaigning in Iowa on Friday.
[link to abcnews.go.com]


Is a well seasoned politician like Bernie Sanders getting down and dirty as is SOP in most campaigns or is he just getting desperate?