When Nixon was impeached, it didn't result in a Republican getting elected in the next election. It got Jimmy Carter elected. The reason is because the majority of people saw that Nixon was not acting in their best interests or in the country's best interests. When Clinton was impeached, a lot of people got pissed off because they saw that the people trying to impeach him were not acting in their best interests or the country's best interests. But that didn't stop a Republican from getting elected in the next election cycle.

If Cheney and/or Bush get impeached, people will see the evidence for themselves and, as with Nixon, the majority of people will see that Bush and Cheney are not acting in the best interests of the country or the majority of Americans, and as with Nixon, I don't think that will result in a backlash against the Democrats by the majority of voters.