Yes, Pelosi is 3rd in line. As you note, there are serious political repercussions for the House Speaker, and by extension the Democrats, for any impeachment move. The Democrats actually have more to gain by letting Bush complete his term, assuming that the war in Iraq remains a mess in November 2008 and perhaps helped by a recession or some other crisis. Above this however is, as I noted before, is the precedent set with the increase of authoritarian powers by the executive branch (and allowed by Congress). Any sane Republican, conservative or not, would not want a Democratic president with the executive powers that Bush now has.