Senator Hillary Rodham Clinton easily won her Democratic primary in New York, winning the chance to stand for re-election in US mid-term polls.
Mrs Clinton's win came as nine states held primary elections
Her win came as nine states held primaries, in which the parties choose candidates for November's elections.
In Rhode Island, moderate Republican Lincoln Chafee defeated a conservative challenger in a fight seen as crucial to the battle for control of Congress.
Democrats need a net gain of six seats to win control of the upper chamber.
They need a net gain of 15 seats to control the House of Representatives, where all 435 seats are up for grabs. There are also 36 races for governorships across America.
Rhode Island is one of Democrats' prime targets, and correspondents say some had hoped that Mr Chafee - seen as the Senate's most liberal Republican - would be defeated by challenger Steve Laffey.
Polls have suggested that Democratic nominee Sheldon Whitehouse would be able to beat Mr Laffey, but would have a much tougher fight against the centrist Mr Chafee.
In the event Mr Chafee took 54% of the vote to Mr Laffey's 46%.
Republicans backed Mr Chafee despite his frequent opposition to President Bush's policies, because he was considered the best "tactical" choice to keep Rhode Island in Republican hands.
In New York, former First Lady Mrs Clinton trounced an anti-war candidate by an 83-17% margin for the chance to face Republican John Spencer in the mid-terms.
New York Attorney General Eliot Spitzer crushed his Democratic rival Tom Suozzi (81-19%) to face Republican John Faso in November, in the race to replace Republican Governor George Pataki.
In the US capital Washington DC, city councillor Adrian Fenty won the Democratic primary for mayor.
Mr Fenty is favourite to replace Mayor Anthony Williams in a city that leans heavily to the Democratic party.
Tuesday's other primaries were held in Arizona, Minnesota, Maryland, Wisconsin, Delaware and New Hampshire.