Vito could have planted leads in the newspapers about McCluskey being a crooked cop, but then McCluskey would have given the reporter and its paper a very hard time, so he wouldn't have done that.

But I think he would have put some pressure on the fact that a cop was acting as bodyguard to a notorious heroin importer. The powers-that-be would have pulled McCluskey off, and Sollozzo would have been vulnerable once again.