So much for star power on Capitol Hill. Backstreet Boy Kevin Richardson — who testified before a Senate Environment and Public Works subcommittee yesterday about mountaintop mining — is the target of Ohio Senator George Voinovich's campaign to limit the time celebrities have been getting in Washington lately. Richardson, who founded the environmental group Just Within Reach, joins other celebs, like Julia Roberts, Michael J. Fox and Christie Brinkley, who have recently taken their causes to Congress.