LAST BLOCK OF US STATES HOLD MID-TERM PRIMARY ELECTIONS
Mike Castle faces a challenge from Tea Party pick Christine O'Donnell in the Delaware senate primary
People in seven states and Washington are voting in the last major block of primary polls to pick party candidates ahead of the US mid-term elections.
Races where conservative Tea Party candidates are taking on established Republican figures are closely watched.
Democrats hope Republicans in Delaware and New Hampshire will be saddled with unelectable, right-wing candidates.
Republicans hope to benefit from anger over the US economy to win both houses of the US Congress in November.
Continue reading the main story
US Elections 2010
A new mood
Q&A: The Basics
The balance of power
So far this year, seven incumbent members of Congress, four Republicans and three Democrats, have been beaten in primary contests, while a number of Republican Party-backed candidates have suffered reverses across the US.
In one keenly-watched race on Tuesday, Delaware Republican Congressman Mike Castle is fending off a surge by Tea Party favourite Christine O'Donnell for the Republican nomination for the US Senate seat once belonging to Vice-President Joe Biden.
Tea Party candidates
Polls indicate Mr Castle would be well positioned to beat his Democratic opponent in November, while analysts view Ms O'Donnell as the weaker candidate for the congressional poll.
In New Hampshire, former state Attorney General Kelly Ayotte faces Tea Party-backed Ovide Lamontagne in the race for the Republican US Senate nomination.
The US capital, Washington DC, will effectively choose its mayor on Tuesday, with incumbent Adrian Fenty expected to be beaten by council chairman Vincent Gray in the Democratic primary.
Mr Fenty's candidacy has been hindered by perceptions among African-American voters that he is more attuned to the needs of the city's affluent whites.
Meanwhile, in New York, veteran congressman Charles Rangel faces New York City voters for the first time since a congressional panel accused him of a series of ethical lapses. Five challengers are vying for his job, though he has a roughly 10 to one advantage in campaign cash.
Hawaii's primary on 18 September is the last of the current election season in the US.