Senate Republicans' latest successful effort to block a campaign finance bill may be a death blow to a White House effort to rewrite campaign rules in the run-up to the midterm elections.

The measure would have imposed new restrictions on political activity by special interest groups, but the 57-41 vote was three short of the total needed to advance the measure.

Democrats swiftly unleashed a coordinated attack saying Republicans defend big banks, big insurance, big oil and other special interests but not the voices of ordinary Americans.

Republicans say Democrats need to put aside their electoral self-interest and start addressing the struggling economy.

The bill had been crafted in response to a Supreme Court decision that said corporations and unions were free to spend their own money on various forms of political activity.

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