Lambert retired in January 2015 after 22 years as executive Director of the Tribal Gaming Commission. As a candidate for chief, Lambert said he would start an office of employee rights, deal with the tribe's drug Problem, focus on tourism and its economic benefits, and protect the rights of the people as a sovereign nation. He also said the government-owned local newspaper, the Cherokee One Feather, was not truly independent despite the free press act, and he intended to make changes to ensure its independence. As one of five candidates, he received 59 percent of the vote in the June 2015 primary.

Lambert suspected previous chief Michell Hicks of misusing tribal funds. In April 2016, Lambert presented results of an audit to the Tribal Council. He asked the FBI to conduct its own investigation.

On May 25, 2017, the Tribal Council found Lambert guilty on 8 of 12 charges. Being found guilty on even one would have been enough to remove Lambert as chief. 9 of 12 members voted for the resolution removing Lambert. Opponents of this action claimed impeachment was done in retaliation for an FBI investigation that Lambert ordered. Among the offenses: Lambert was accused of signing a contract with Harrah's Cherokee that involved the casino renting rooms in Lambert's hotel, signing other contracts without tribal council approval, and improper hiring practices. Lambert and his attorney said Lambert did nothing that would justify impeachment. Vice Chief Richard Sneed replaced Lambert immediately.