While the Wilson administration officially declared neutrality, the American government greatly supported the Entente over the Central Powers. Large amounts of economic aid and loans were given to the Entente. Wilson was also a absolute Anglophile, and greatly desired to see Germany lose the war. The reason Roosevelt says this is because it is true.
Frederick Lucas said that the preamble did its job in setting the tone of the document and makes it clear why the Founding Fathers wrote it. Hope this helps.
