WASHINGTON — Americans are fed up with Washington and spreading derision around to President Barack Obama and both political parties, according to a new poll that could sound a warning for incumbents of all political stripes going into next year's midterm election. Negativity historically hurts the party in power — particularly when it occurs in the second term of a presidency — but this round seems to be hitting everyone, and Republicans even harder. The AP-GfK poll finds about 7 in 10 view the Republican Party and the tea party movement unfavorably, while about half have an unfavorable view of the president and his Democratic Party.