The U.S. Chamber of Commerce is launching a TV campaign against former Maine governor Angus King’s independent bid for the Senate, accusing him of being the “king of spending” in an effort to boost a long-shot Republican candidate.

The Chamber is the first conservative group to wade into the Maine Senate race, which had previously been considered a safe bet for the still popular King. With advertising inexpensive in Maine, officials familiar with the Chamber’s campaign suggested that the new ad wars could serve as an opening volley to see if King’s popularity can be dented and, if so, may soon be followed with campaign ads from other conservative groups criticizing King’s record as governor.

“While King was governor, state spending skyrocketed to $2.6 billion; the king of mismanagement, when King left office, he left Maine with a $1 billion shortfall,” the narrator says in the Chamber’s ad, which will begin airing Thursday.

Chamber officials declined to address the total cost of the ad campaign, but it is expected to run for nearly 10 days.

This is one of 11 Senate races in which the Chamber has now launched TV ad campaigns through its political arm, which can run its operations without disclosing the donors financing them. Maine, however, marks the riskiest bet yet because the other 10 races are considered the marquee match-ups that will decide which party controls the Senate next year. After Sen. Olympia Snowe (R-Maine) surprised both parties with her announcement that she would not seek re-election, Republicans and Democrats scrambled to find candidates for what had previously been considered an easy race for the popular Snowe.

Charlie Summers, serving as Maine’s appointed Secretary of State, has lost three previous bids for a seat in the House. He won the GOP primary last month, as Democrats nominated a little known state senator, Cynthia Dill.

King’s entrance into the race prompted other prominent Democrats to back away from running, leading strategists in both parties to believe King’s unspoken plan is to support the Democrats. In Washington the Democratic Senatorial Campaign Committee has done nothing to support Dill’s nomination, and the independent Rothenberg Political Report recently graded the race as shifting “toward Democrats — sort of” as it declared King was the clear favorite.

A Portland Press Herald poll gave King 55 percent of support to 27 percent for Summers, with just 7 percent supporting the Democratic nominee.

King’s campaign theme is to run above the fray of the tit-for-tat tactics that usually accompany a Republican-versus-Democrat campaign, suggesting that what Washington needs is middle-of-the-road common sense. “Everywhere I go in Maine . . . it’s all they want to talk about. They want me to go down there and talk some sense into those people — go down there and make it work,” he told the Washington Post last month during a campaign stop in Portland.

Despite King’s popularity, some Republicans question whether he is ready for a 21st century campaign. He won a gritty, three-way race in 1994 by knocking off Susan Collins, who would later win a seat in the Senate, and Joe Brennan, a former governor and former congressman. Independently wealthy, he coasted to re-election in 1998 and then retired from politics as his term ended in 2002, until Snowe’s surprise retirement announcement.