According to the Atlanta-Journal Constitution: “There is strong evidence that in at least three instances, prosecutors were removed because they had failed to use their office to investigate and indict Democrats, or had been too aggressive in indicting Republicans.”
The strongest example suggesting that politics are behind the dismissals, is that of Carol Lam, the fired attorney from San Diego. The Los Angeles Times cites a CBS Face the Nation interview in which, “Sen. Dianne Feinstein (D-Calif.) revealed evidence that Lam had notified Washington about search warrants in a Republican corruption case last year. Soon thereafter, a top Justice Department official in Washington wrote to the White House about a ‘real problem we have right now with Carol Lam.’"

The Los Angeles Times reports that similar suspicion has been raised over the case of David Iglesias, the former U.S. attorney of New Mexico. “Democrats charge that his departure is linked to veiled attempts by two Republican lawmakers to speed up action on a Democratic corruption scandal before last year's midterm election. “

The Atlanta-Journal Constitution challenges the White House’s cited reason of poor work performance for the dismissals, pointing out: “That explanation almost immediately unravelled. Most of the eight had sterling job-performance reviews and were very well regarded in their regions.”