While Dick Cheney has been highly instrumental in facilitating anti-Bush sentiment, it must be noted that George Bush himself deserves the lion's share of credit for his own low poll numbers. Indeed, George Bush's low approval ratings have helped drag down the Republican Congress's poll numbers in concert. George Bush is most certainly the goose that keeps laying rotten eggs in the lap of the Republican Congress.
This brings up the question of the rationale of pushing for impeachment. I personally am a strong proponent of the idea, because no one should be above the law, including the president. However, there is something to be said for the counter argument that impeachment of Bush and Cheney would be like killing the goose that laid the rotten eggs in the Republican's lap. George Bush and Dick Cheney are the best thing that has happened to the Democratic Party since John F. Kennedy was elected. They are the gift that keeps on giving over and over and over again. No amount of rhetoric coming from the Democrats could have achieved the same goal.
I should mention that this line of thinking might eventually seep into the clouded minds of Republicans, who must at this point start to recognize the immeasurable harm that Bush and Cheney have done to their party. In fact, if they were smart, they would help the Democrats initiate impeachment against both of these men. It would be the best thing they could do for their party, while at the same time having the beneficial side effects of being good for the country and the world at large.
It's a tough choice for Democrats, but I still say that we are a nation of laws, not men, and as such we need to cook the goose and move on.