Washington ? Deep-pocketed unions, business groups and others are spending heavily in the year’s early primaries, including a staggering $9.6 million to influence a Democratic Senate race in Arkansas, adding volatility to a struggle for control of Congress that has already produced its share of surprises.

The flood of money comes under campaign laws that bar coordination with the candidates and sometimes allow donors to hide their identity. Outsiders can be left guessing about the true political objective.

According to campaign professionals in both parties, these independent efforts can achieve their stated purpose — or actually hinder the candidate they are designed to help.

“They have the opportunity to help if they are complementing the issue debate that’s ongoing,” said Carl Forti, a former top official at the National Republican Congressional Committee.

“But you also run the risk of a third-party group coming in on a message that’s not really been an issue in the campaign and doing more harm than good by” changing the subject said Forti, who now works for an independent organization, American Crossroads, created to help Republicans.

However controversial or even effective, these efforts mirror struggles unfolding inside both major political parties as they set their candidate lineups for the general election in November.

The assault by tea party activists and other conservatives on the Republican establishment has toppled Utah Sen. Bob Bennett and is playing out in television ads, mass mailings and other efforts by outside groups in the GOP senatorial primary in Kentucky this week. Anything but subtle, a commercial paid for by America Future Fund, a Des Moines, Iowa-based organization, strongly suggests that Republican senatorial front-runner Rand Paul is crazy.

Among Democrats, several unions have invested millions to deny Arkansas Sen. Blanche Lincoln renomination on Tuesday, a move that puts them at cross-purposes with party leaders and an approach that other labor groups have shied away from.

“It’s time to send a message of accountability,” said Jon Youngdahl, political director for the Service Employees International Union, citing the lawmaker’s votes in favor of trade legislation opposed by organized labor and her opposition to important parts of a union-backed agenda.

Ironically, two business-oriented organizations are spending heavily to help Lincoln.