The FBI Director may have a single ten-year term limit but it is a presumptive ten-year limit. The Director may be impeached by Congress for "high crimes and misdemeanors" (this is not defined by the Constitution) if charged by the House of Representatives and then removed by a two-thirds vote of the Senate but the President has the authority to fire him for any reason even without cause.
President Clinton, for example, fired William Sessions after he refused to resign back in 1993. Clinton did not have to rely on a Congressional impeachment process.
According to a 2014 report by the Congressional Research Service, “there are no statutory conditions on the President’s authority to remove the FBI Director" (http://bit.ly/2n8Mflp).
Comey has committed violations that prove he is a partisan politician and not a fair and honest Director of the FBI. He admitted that Hillary Clinton's server was used illegally but then he gave her a slap on the wrist. He violated the Hatch Act Reform Amendments of 1993 a few months later when he tried to influence the 2016 Presidential election only a week prior to Election Day (against department policy of both the Justice Department and the FBI) after he said he was reopening the Hillary Clinton email investigation only to close it again just a couple of days prior to Election Day when he announced that Hillary should not be prosecuted.
