The process was guaranteed to be a level playing field by the DNC charter (Article 5, Section 4):
In the conduct and management of the affairs and procedures of the Democratic National Committee, particularly as they apply to the preparation and conduct of the Presidential nomination process, the Chairperson shall exercise impartiality and evenhandedness as between the Presidential candidates and campaigns. The Chairperson shall be responsible for ensuring that the national officers and staff of the Democratic National Committee maintain impartiality and evenhandedness during the Democratic Party Presidential nominating process.
In the conduct and management of the affairs and procedures of the Democratic National Committee, particularly as they apply to the preparation and conduct of the Presidential nomination process, the Chairperson shall exercise impartiality and evenhandedness as between the Presidential candidates and campaigns. The Chairperson shall be responsible for ensuring that the national officers and staff of the Democratic National Committee maintain impartiality and evenhandedness during the Democratic Party Presidential nominating process.