Republican John McCain attacked Democratic rival Barack Obama for breaking a pledge to rely on public funds, instead of private donations, in their presidential race. Obama's decision Thursday to forgo public funds will allow him to continue his record-breaking fundraising machine that is bound to generate much more than the $84 million he would have received in government money. But by abandoning his earlier commitment, Obama also risks damaging the image he has cultivated as a fresh candidate who would change the money-tainted ways of Washington. McCain said Thursday he will rely on public financing and criticized Obama for backtracking. "This election is about a lot of things. It's also about trust. It's about keeping your word," he told reporters while campaigning in Iowa.