Yes, the DNC failed Americans by showing bias against Bernie Sanders. The job of the DNC is to remain neutral during the election process, but several staffers showed clear bias against Bernie Sanders that violated the trust of the American people and the Democratic Party. They allowed their distrust of Bernie Sanders, an Independent and outsider in the Democratic Party, to trump their professionalism and duty. They did not steal the nomination or influence the election, but they still betrayed the trust of Sanders supporters who expected equal treatment and even Clinton supporters who expected a fair contest.
WikiLeaks released many thousands of emails that show the Democratic National Convention (or DNC) unfairly tipped the primary balance in favor of Hillary Clinton. This is a serious betrayal in the eyes of Bernie Sanders supporters, and rightly so: it shows that they (and other Americans) can no longer believe in a fair electoral process.
The Democratic National Committee betrayed Bernie Sanders and the American public by showing bias toward the Clinton campaign. The DNC is supposed to be a neutral party when it comes to primary campaigns; not choosing a side to support until a candidate is nominated. However, the DNC broke this trust with voters by betraying Bernie Sanders supporters.
By showing bias they did indeed betray both Bernie Sanders, his supporters, and the wider American public. Politics is a dirty game though and this is how people behave. Lots of backstabbing and shady deals go on. People make up things others said and use whatever horrible tactics they can do. Showing bias is another thing that shouldn't have happened, add it to the list of bad political moves, it's a big list that's for sure.