You really do have to wonder exactly what Senators are afraid of
A top conservative Capitol Hill staffer tells Politico that more than 70 senators would oppose Bush’s escalation if their vote matched their comments in private meetings. “The White House is trying to but they really don' know how to handle this,” the staffer said. Digby attempts to answer that question here
It's a great post which references two articles by Rick Perlstein examining the history of the political resistance to the Vietnam war. The short version is that Republicans have been successful in spinning the end of Vietnam as occurring because the dirty hippies stopped support prematurely, and that Democrats are wimps. That political tag is seen as poison and no one wants to be tagged with it. Unfortunately, as Perlstein points out quite well,
this meme is totally wrong and not at all supported by the facts.
Take a short stroll down memory lane (if you're old enough) and read Digby and Perlstein. Their recollections match mine in that it was a completely bipartisan decision to get out of Vietnam, and that we got out for good reason.