WASHINGTON, Sept. 14 (Xinhua) -- A candidate backed by the ultraconservative Tea Party won Tuesday the Republican primary in U.S. state of Delaware, showing the strength of the movement as well as voters' antipathy toward the establishment.

Christine O'Donnell won in Delaware Senate primary, defeating nine-term Representative Michael Castle, one of remaining moderate Republicans in Congress.

However, O'Donnell's win could spell doom for Republican's bid to win the Senate seat vacated by Vice President Joe Biden, as Castle, a popular former governor, had been expected to defeat Democratic nominee Chris Coons.

U.S. voters in seven states and the District of Columbia on Tuesday cast their votes in primaries. In New Hampshire, it's also Tea Party against Republican establishment, as former state attorney general Kelly Ayotte trails the Tea Party favorite Ovide Lamontagne.

The trend shows voter antipathy toward the establishment, but by going to the right, Republicans could alienate moderates, and hand Democrats a chance to hang on to their majority in Congress.