The Chicago Tribune in late June of '42 reports the mass killing of Jews. Like many other newspapers, the Tribune puts it on page 6 or 7 in a tiny, little article. You either missed it, or if you saw it, you would say the editors don't think this is true. If they thought this was true, this would be on the front pages. Only a few of papers did put the story on the front page, including the Pittsburgh Courier.
The dominant idea in the American government is any act of rescue will be a diversion from the war effort. Both could've been done at the same time. In spite of that, a group of government officials supports and finances rescue operations. Allied soldiers begin to liberate concentration camps and find mass graves. The public sees the sheer scale of the Holocaust.