Mier's helped cover up Bush's National Guard duty or lack thereof

While Miers was chairwoman of the commission, the former executive director filed suit, claiming that he was fired to ensure that allegations were not made public that then-Gov. Bush had gained acceptance into the Texas Air National Guard in 1968 as a result of political favors. At roughly the same time -- and also during her tenure as chairwoman -- Miers was paid by Bush's re-election campaign to investigate Bush's Guard record in order to deflect allegations that Bush received preferential treatment.
Of course the whole story is available at Media Matters