This is actually quite a difficult question to answer for the simple fact that it is always problematic to measure what effects public opinion.

However, you are talking here about Yellow Journalism, in which american newspaper editors (more specifically Pulitzer and Hearst) fought in order to public the most spectacular, bloody and jingoistic articles in order to attract the large readership needed for the 'penny press' to succeed.

While it is hard to say if newspapers influenced the decision to declare war, it could be argued that by printing stories reinforcing a nationalist rhetoric, they gave moral caution to a militarist solution...

Joyce Milton's book The Yellow Kids: Foreign Correspondents in the Heyday of Yellow Journalism is a very good book on that subject, and so is Joseph Campbell's book Yellow Journalism: Puncturing the Myths, Defining the Legacies.