And, what Bush has done already ISN’T grave?

I simply do not get Barack Obama’s justification for opposing Bush or Cheney impeachment Last week, he said:

“I think you reserve impeachment for grave, grave breaches, and intentional breaches of the president's authority,”

And illegal wiretaps, lying the country into war, possible obstruction of justice with Libby’s commutation, and blatantly politicized district attorney firings aren’t “grave, grave breaches”?