Here's a link to the entire Politico article:
As the Democratic primary season nears a close, the candidates have talked about dozens of policies, fended off a host of attacks and studiously avoided one topic: the impeachment of President Clinton.
Whether that’s a product of self-control or self-preservation, the tactical decision by Hillary Rodham Clinton’s opponents to steer clear of any direct reference to what may have been the defining moment of the Clinton White House seems remarkable given the duration and intensity of the 2008 primary campaign.
While Republicans signaled early that it would be a major issue should she win the nomination, it has been a forbidden topic for her primary rivals since early 2007, when David Geffen, a former Clinton ally and a Hollywood supporter of Barack Obama, felt the wrath of the Clinton camp — and received a scolding from the Obama campaign — after raising it in an interview.
The reasons for the silence are both obvious and subtle.