It's called "the opposition"

The OPPOSING party is called the OPPOSITION for a reason.

They OPPOSE the incumbents.

It's a vital and valid role that serves a valuable purpose.

It's healthy to have critics evaluating, testing and fighting you.

It makes you better, tougher and stronger. In fact, a vigorous opposition forces you to refine and improve your proposals and more clearly articulate your beliefs.

The absence of an opposition is why every dictatorship eventually falls, while democracies survive and prevail.

Why are people shocked when the opposition opposes the other party?

http://andrewsullivan.theatlantic.com/the_daily_dish/2009/02/the-gop-has-dec.html

By the way - - does Andrew Sullivan have any recollection of the personal, nasty, gossipy things he wrote about Bill and Hillary Clinton, or George W. Bush, when Sullivan was part of the opposition? I don't remember any of these Obama folks ever rolling over "because it's in our interest for the president to succeed". (Quick reminder - - Sullivan used to spread "Hillary's a lesbian" and "Palin's not really her youngest son's mother" stories.)