WASHINGTON — The U.S. Chamber of Commerce is hammering Maine independent candidate Angus King and Democratic incumbents in Montana and Ohio in a new round of ads designed to help Republicans grab control of the Senate.

The ads, which begin airing Tuesday, focus on King’s fiscal record as governor, criticize Montana Sen. Jon Tester on health care and energy and weigh in against Ohio Sen. Sherrod Brown for his votes on energy. Tester and Brown have been top targets of the Chamber for months as the nation’s largest business lobbying group has spent tens of millions of dollars in some eight Senate races and dozens of House contests.

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The Republicans need a net gain of four seats to capture control of the Senate, and the loss of the Maine seat to independent Angus King would complicate its prospects AP

King, seen as likely to side with Democrats if he wins, was the subject of a Chamber ad in July.

Rob Engstrom, national political director for the Chamber, declined to say how much the group was spending for the ads that will air for 10 days to two weeks, simply calling them a “massive buy.” In the July round, the Chamber spent more than $914,000 against Brown, $257,000 against Tester and $400,000 opposing King, according to independent expenditure reports filed with the Federal Election Commission.

With Democrats holding a slim majority in the Senate – 51-47, plus two independents who usually vote with the Democrats – the National Republican Senatorial Committee and GOP-leaning groups are investing tens of millions in roughly a dozen races, some with vulnerable Democratic incumbents or open seats.

Missouri used to be part of the calculation, but Republican Rep. Todd Akin’s comments last month about women not getting pregnant from “legitimate” rape led many in the Republican Party to abandon the candidate. That has freed up millions of dollars, allowing the party to spend elsewhere.

Republicans see a potential opening in the Maine race to replace Sen. Olympia Snowe, who surprised Republicans earlier this year with her decision to retire. The Republicans need a net gain of four seats to capture control of the Senate, and the loss of the Maine seat would complicate its prospects.

King is facing Democrat Cynthia Dill and Republican Charlie Summers.

The Chamber ad lampoons King with the line “it’s good to be king,” arguing that spending skyrocketed during his tenure and that Maine faced a $1 billion shortfall when he left office.

“Mainers can’t afford to send this King to Washington,” the ad says.

King has responded to the spending by outside groups with a spot that shows Godzilla, the famed Japanese movie monster. The former governor talks about “some folks from away” trying to convince voters that he’s a monster. King says he cut taxes and fixed bad roads in the commercial, which ends with Godzilla burping.

Earlier this month, Erskine Bowles, a Democrat best known these days for his budget-cutting plan with Republican Alan Simpson, endorsed King and said he had experience balancing eight budgets during his time in office.

The Chamber ad against Tester is a report card that gives him a failing grade for casting a deciding vote for “government-mandated health care,” a reference to President Barack Obama’s health care overhaul law. Last month, Tester unveiled an ad highlighting his breaks with the Obama administration on the environment and energy as well as his opposition to the Wall Street and auto bailouts.

Tester is locked in a close race with Republican Rep. Denny Rehberg.

The commercial against Brown argues that his votes on energy will lead to greater dependence on foreign oil, more layoffs and higher prices at the pump. Brown has opposed tax breaks for big oil companies. The Democrat holds a slight edge in his race against Republican challenger Josh Mandel.