Complex sentence: Campbell was not in fact involved with the company, and the affair cost Foraker votes; a congressional committee after investigation in 1891 cleared all of those whose signatures had ben reproduced, but blamed Foraker for using the documents without verifying their authenticity.
Split into simpler sentences: Campbell was not in fact involved with the company, and the affair cost Foraker votes. However, it blamed Foraker for using the documents without verifying their authenticity.