Didn’t the Three Witnesses deny their testimonies about the Book of Mormon?

In the introduction to the Book of Mormon there is section entitled “The Testimony of the Three Witnesses”  This testimony was given by three men–David Whitmer, Oliver Cowdery, and Martin Harris–each of whom saw the plates from which Joseph Smith translated the Book of Mormon.  According to their account, they gathered with Joseph Smith to pray in the woods and while praying an angel appeared to them and showed them the plates and other artifacts. 

Over the next several years, these three witnesses faced many challenges and left the Mormon Church.  Two, Harris and Cowdery, later returned humbly repenting of their mistakes and pride which had driven them out of the Church.  Whitmer never rejoined the Mormon Church, but he never denied his testimony.  Instead, he claimed that everyone else in the Church had gone wrong, but that the Book of Mormon and his testimony were still true. 

Anti-Mormon critics have tried to argue that one or all of these denied their testimony.  However, the circumstances that led these men out of the Church either by choice or by excommunication were unrelated to the Book of Mormon.  Harris was excommunicated because of problems in the Church during a financial crisis.  He became offended and left, but in 1870 he rejoined the Mormon Church and moved to Utah where he died many years later.  Cowdery likewise left the Mormon Church because of economic and political differences in 1838 and even accused some other members of the Church with adultery.  In 1847, he rejoined the Church and died will crossing the Great Plains with the Mormon pioneers.  Whimter, like Harris, left the Church during problems caused by a nation-wide financial crisis in 1837.  He moved away and opened a business in Missouri where he remained until his death.  Though he never rejoined the Mormon Church, he nevertheless maintained that his testimony of the Book of Mormon was true, but that the Mormon Church had strayed.  Shortly before his death, he even took out a newspaper ad testifying about the Book of Mormon.