Why did President Mckinley finally send the U.S.S. Maine to Havana?

In addition to the information above, William Randolph Hearst, newspaper magnate and yellow journalist extraordinaire, had widely published reports of the atrocities against the Cuban people at the hands of the Spanish.  While the reports were exaggerated, they were more or less true, and a moral outcry that began in the churches of the northeast and among socialists and progressives put some populist pressure on McKinley to send a message to Spain, or take some action that would suggest America would not stand idly by no matter what Spain did.

McKinley's primary motivation was, as stated above, to protect Americans and their business interests in Cuba, but there was a public political motivation and benefit for him as well.