WASHINGTON — Virtually unknown a month ago, Christine O’Donnell rode a surge of support from tea party activists to victory in Delaware’s Republican Senate primary Tuesday night, dealing yet another setback to the GOP establishment. A second insurgent led narrowly for the GOP nomination in New Hampshire.

O’Donnell defeated nine-term Rep. Mike Castle, a fixture in Delaware politics for a generation and a political moderate. Republican Party officials, who had touted him as their only hope for winning the seat in the fall, made clear as the votes were being counted they would not provide O’Donnell funding in the general election campaign.

She enters the fall campaign as an underdog to Chris Coons, a county executive who was unopposed for the Democratic nomination. The Republican state chairman, Tom Ross, said recently she “could not be elected dogcatcher,” and records surfaced during the campaign showing that the IRS had once slapped a lien against her and that her house had been headed for foreclosure. She also claimed falsely to have carried two of the state’s counties in a race against Vice President Joe Biden six years ago.

With unemployment high and President Obama’s popularity below 50 percent, Republicans said a run of hotly contested primaries this spring and summer reflected voter enthusiasm that will serve the party well in the fall. The GOP needs to win 40 seats to take the House and 10 for control of the Senate.

Democrats countered that the presence of tea party-supported Republicans on the ballot on Nov. 2 would prove costly to the GOP. That proposition will be tested in seven weeks’ time in Senate races in Nevada, Colorado, Florida, Kentucky – all states where establishment Republican candidates fell in earlier primaries – and now Delaware.

In the other marquee race of the night, for New Hampshire’s Republican Senate nomination, lawyer Ovide Lamontagne led former Attorney General Kelly Ayotte, 40 percent to 38 percent, with votes counted from more than a third of the precincts.

Lamontagne, a former chairman of the state Board of Education, campaigned with the support of tea party activists, while Ayotte had a coalition of establishment Republicans, former Alaska Gov. Sarah Palin and other conservatives.

The winner will face Democratic Rep. Paul Hodes, who is giving up his seat in the House to run for the Senate.

Nearly complete returns from Delaware showed O’Donnell with 53 percent of the vote. “Don’t ever underestimate the power of ‘we the people,’” she told supporters who cheered her triumph.

But Coons issued a statement moments after Castle’s defeat. “We cannot let Joe Biden’s seat fall into ultraconservative hands,” he said.

Democratic New Hampshire Gov. John Lynch rolled to renomination for a fourth term, and he will face John Stephen, a former state health commissioner who won the GOP line on the ballot easily.

In New York, 40-year veteran Democratic Rep. Charles Rangel easily won renomination in his first time on the ballot since the House ethics committee accused him of 13 violations, most of them relating to his personal finances.