When the Party was collapsing. He ran on vaguely Leftist campaign in '92. He pledged massive healthcare reform, he pledged to oppose free trade unless it had all sorts of regulations, he railed against Paul Tsonga's pro-business policies, he wanted to drastically raise taxes on the rich, and he was a 60's kid who protested Vietnam. That was why so many felt betrayed by Clinton, he didn't run as far to the right he governed. Of course he didn't really have much choice in the matter after we lost both houses and his approval rating plummeted, so I don't blame him too much.
LBJ never shied away from his commitment to the American poor, even during his campaign. Read his acceptance speech, not one word of Goldwater, but a lot of stuff about ending poverty and bring prosperity to all Americans. JFK was strongly supported by leaders of the Civil Rights movement, which was controversial enough. He didn't need to be anymore aggressive than that, the Party was splitting in two over the issue and it wasn't time to announce some grand new mission before the old one had run it's course.
As for FDR, while he did initially run on banking reform and fixing the economy, that's because those were the biggest issues during the Great Depression. Banks were folding left and right, people couldn't trust them anymore. Few had jobs, and fewer still had ones that were acceptable. Soon after that Huey Long and socialist activists began pushing for social reforms, and FDR was in real political trouble. He co-opted the most feasible of their agenda, and many of those issues are the ones he's best remembered for. The fact that he did this while in office rather than before hand is unsuprising, as the political strength of socialism grew as the Depression went on, so FDR had to address their concerns.
I'm just saying the Party should proactively deal with the general disatisfaction with the direction of the Party. They don't necessarily have to do it now, but they should do it soon before the Bush* shock wears off. Besides, if Bush* proved anything it's that you don't have to govern as you campaigned.
http://www.geocities.com/rickmatlick/nomalbj.htm