Clinton removed 93 US Attorneys at the beginning of his term. President Bush, removed 91 US Attorneys at the beginning of his term. It is historically accurate that Presidents will name new US Attorneys at the beginning of their terms. Many US Attorneys resign as the appointing Presidents term in office is coming to a close. It has also been shown, historically, that rarely do US Attorneys get replaced in the middle of a President's term.
What is different about these US Attorneys, is their activities prior to their resignation. During the Bush Adminstration, US Attorneys were investigating Democrats 81% of the time, and Republicans 19% of the time.
One was removed to be replaced with Karl Rove's buddy.
One put Duke Cunningham on trial and received a conviction.
One would not bring indictments against Democratic candidates before the 2006 election, despite phone calls (pressure) from a US Senator and US Representative.
One wouldn't give a satisfactory answer about looking into Washington State Voter fraud charges - where a Democratic Candidate won a close election.
http://talkingpointsmemo.com/usa-timeline.php
And, let us not forget the admendment placed into the Patriot Act by Senator Spector's aide,
without Senator Spector's knowledge, that allows the President to appoint an replacement US Attorney
without the Advice and Consent of the Senate.
As for Mitt Romney .... gee, the guy has lived in Massachusetts for the past two decades ... and on the campaign trail he uses it as the butt of his jokes. Oh, the irony. Republicans rooting for a Massachusetts Liberal Flip-Flopper for their Presidential candidate.