The Tea Party Express has defeated the GOP three times

Within the fragmented tea-party movement reshaping American politics, one group has proved especially skilled at winning elections.

The Tea Party Express played a central role upending Republican primaries in Nevada, Alaska and, this week, Delaware, raising millions of dollars to help topple candidates favored by GOP bosses.

Most groups in the populist tea-party movement channel their energies through grass-roots organizing and social networking. The Tea Party Express, by contrast, is driven by a Republican consultant with a more conventional approach.

Sal Russo, 63 years old, a longtime California GOP operative and former aide to Ronald Reagan, runs Tea Party Express out of his Sacramento, Calif., consulting firm.

As chief strategist, he sends out solicitation emails to the group's list of 400,000 addresses—carrying subject lines such as "Harry Reid Doesn't Want You to See This"—and crafts the messages carried in TV and radio ads and in mailings.

"The establishment in the Washington beltway gets it wrong all the time," Mr. Russo said. Republican Party leaders too often recruit candidates who fit the ideological profiles of their states and districts, he argued, rather than seeking out dynamic, new voices.

"The answer is having bold colors, not pale pastels, to create a clear contrast with the opposition," he said.

That, he added, was what the Tea Party Express did best. It also picks its shots in small states, where limited spending can turn the tide.

Sen. Lisa Murkowski of Alaska sees it differently. She called the Express "an outside extremist group" that "hijacked" the state GOP. The Express spent $590,000 in support of her opponent, Joe Miller, in Alaska's Aug. 24 primary for the Republican Senate nomination. Mr. Miller won.

In Delaware, antipathy toward the group went farther. The Delaware Republican Party was backing Rep. Mike Castle in this week's GOP Senate primary. The Express supported Christine O'Donnell, the eventual winner. The state Republican party has filed a complaint with the Federal Elections Commission alleging illegal coordination between Ms. O'Donnell and the group—a charge denied by both.

GOP officials are hoping the Express will be as committed to defeating Democrats in the general election as it was to beating up Republicans in the primaries.

"Ultimately, for those who care about limited government and lower spending, winning back a Republican majority in the Senate should be a shared priority," said Brian Walsh, spokesman for the Republicans' Senate campaign committee.

Mr. Russo said his group was still laying specific plans but would back Mr. Miller, Ms. O'Donnell and Nevada Senate candidate Sharron Angle in their general-election races.

The tensions between the Tea Party Express and Republican leaders underscore how the rise of the tea-party movement, which is critical of government spending and many Obama administration policies, has shifted power from GOP officials in Washington to outside activists and groups who operate by their own playbooks.

Mr. Russo created the group last year as an offshoot of his political action committee, Our Country Deserves Better, formed to oppose Barack Obama when he was running for president. The PAC has raised $5.3 million in the 2010 election cycle.