Billionaire entrepreneur Elon Musk has officially stepped down from his role as head of the Department of Government Efficiency, ending his brief but high-profile stint as a special government employee.Walter Isaacson, author of the biography "Elon Musk," believes the SpaceX and Tesla mogul is leaving deeply "frustrated" by the limits of Washington.Isaacson says Musk's time in government wasn't a strategic move for his businesses but a personal mission to fix what he saw as a failing system."Whether it's him taking over Twitter or dealing with Tesla's crisis or SpaceX, you see that all-in intensity," Isaacson said. "Sometimes it works. Sometimes it doesnt. But hes all-in."WHAT'S NEXT FOR DOGE AFTER ELON MUSK'S DEPARTURE? 'ONLY JUST BEGUN'According to Isaacson, that mindset ultimately clashed with the limitations of government."You cant do that in government," he said. "Because he doesnt own the federal government."MUSK OFFICIALLY STEPS DOWN FROM DOGE AFTER WRAPPING WORK STREAMLINING GOVERNMENTMusk's frustration was on display earlier this week when he criticized President Donald Trumps recently House-passed spending bill. During an appearance on "CBS Sunday Morning," Musk argued the bills increased spending worsens the national deficit and "undermines the work the DOGE team is doing."The comments have sparked speculation of a growing divide between Musk and Trump, who had previously aligned in their push to reduce government waste.Isaacson says the criticism wasnt personal but aimed at the broader system."He is frustrated that even the Republicans in the House and the Senate have been captured by Washington interests," he said.DAVID MARCUS: WHAT AMERICA OWES ELON MUSK AFTER DOGEMUSK NOT LEAVING YET, WRAPPING UP WORK ON SCHEDULE ONCE 'INCREDIBLE WORK AT DOGE IS COMPLETE': WHITE HOUSEThe One Big Beautiful Bill Act narrowly passed the House, with all Democrats and two Republicans voting against it. Several senators from both parties have also voiced concern over the bills lack of spending cuts.Despite their policy disagreements, Elon Musk and President Trump held a joint press conference on Friday before Musk returned full-time to his roles atTesla, X, and his other companies.PRESIDENT TRUMP TEASES LAST DAY, BUT NOT REALLY FOR ELON MUSK AT DOGE: OVAL OFFICE PRESSER SET FOR FRIDAYMusks time at DOGE officially ended at the legal 130-day limit for someone with a special government employee designation. In a post on X, Musk echoed Trumps sentiments, thanking the president for the opportunity to serve the country."As my scheduled time as a Special Government Employee comes to an end, I would like to thank President @realDonaldTrump for the opportunity to reduce wasteful spending," Musk posted on Wednesday."The @DOGE missionwill only strengthen over time as it becomes a way of life throughout the government."CLICK HERE TO GET THE FOX NEWS APP