(CNN) - A leading Tea Party organization that supported Republican Senate nominees Sharron Angle of Nevada and Mike Lee of Utah, and which gave a big boost to Senate candidate Joe Miller of Alaska, says it's coming to the aid of Christine O'Donnell of Delaware.
Tea Party Express, one of the best known national Tea Party groups, says it will go up with commercials in support of O'Donnell, who is facing off against Rep. Mike Castle in the battle for Delaware's GOP Senate nomination.
Listen: CNN's Paul Steinhauser and Dick Uliano take a look at the Tea Party movement in Delaware.
Tea Party Express spokesman Levi Russell tells CNN that his group hopes to start running two pro-O'Donnell commercials on television in Delaware by the end of the week. Russell says Tea Party Express will spend around $250,000 for the initial ad buy, and says "we'll see where it goes from there."
The group endorsed O'Donnell in late July but the ads are the first the organization has produced in support of O'Donnell. In backing O'Donnell, Tea Party Express said the candidate has "established a reputation as a strong voice for conservative constitutionalist principles consistent with the ideals of the Tea Party movement," and they criticized Castle.
"Mike Castle is so liberal he voted for Barack Obama's agenda nearly 60 percent of the time," says the narrator in one of the two ads in the works. Russell says that besides the two TV commercials, three radio spots are also in production.
Russell tells CNN that "this race is another example, much like Nevada and Alaska, where a true conservative is going toe-to-toe with a RINO [Republican in name only] Republican backed by the establishment."
Castle is a popular nine-term congressman and former two-term governor who's considered much more moderate than O'Donnell, a conservative commentator and marketing consultant who ran unsuccessfully for the Senate in 2006 and 2008.
Castle defeated O'Donnell in May at the state GOP convention and is backed by the state party chapter. The Republican Party of Delaware describes O'Donnell as a "perennial candidate" and Chairman Tom Ross terms the involvement of the Tea Party Express as "unfortunate." A Republican source tells CNN that O'Donnell's trying to piggyback off the Tea Party movement.
The winner of November's general election will fill out the remaining four years of Vice President Joe Biden's final term in the Senate. Biden stepped down from the Senate after his election in November 2008 as vice president. Former Biden aide Ted Kaufman was named as an interim replacement. Kaufman is not seeking a full term.
After much speculation that he would run for his father's old seat, Delaware Attorney General Beau Biden announced in late January that he would instead run for re-election as his state's top lawyer. Nine days after the younger Biden's announcement, New Castle County Executive Chris Coons officially announced his candidacy for the Democratic Senate nomination. He is the presumptive Democratic Senate nominee in a race political handicappers consider a prime pick-up possibility for the GOP.
The involvement of the Tea Party Express in assisting O'Donnell comes after the group poured nearly $600,000 to help Miller, who leads Sen. Lisa Murkowski by 1,668 votes, according to unofficial results from last Tuesday's GOP Senate primary in Alaska. Counting of up to 15,000 absentee ballots begins Tuesday.
Tea Party Express is one of the most recognized national Tea Party organizations thanks to its three high-profile bus caravans and rallies. The Tea Party Express has also become a major player in Republican politics, spending hundreds of thousands of dollars on ads for Republican Senate candidate Scott Brown in Massachusetts, who in January upset Democrat Martha Coakley in a special election to fill the late Sen. Ted Kennedy's seat.
More recently, the organization helped the little-known Angle win the Republican primary in Nevada to face Senate Majority Leader Harry Reid, endorsing her and spending about a half-million dollars on ads.
The group also targeted incumbent Republican Sen. Bob Bennett in Utah for his vote on the Troubled Assets Recovery Program and helped defeat his bid for a fourth term. It then backed underdog Mike Lee's successful primary campaign and Lee now appears to be a shoo-in to win the general election in November and join the Senate next year.
This summer, the National Tea Party Federation, which seeks to represent the Tea Party political movement around the country, expelled the Tea Party Express because of an inflammatory blog post one of its leaders, Mark Williams, wrote responding to criticism from the NAACP. Williams later stepped down as spokesman for Tea Party Express.
Follow Paul Steinhauser on Twitter: @psteinhausercnn