Tesla shares slipped 5% in U.S. premarket trading Friday, extending losses from earlier in the week. On Wednesday, Tesla shares slumped 8% to record their worst day since before Donald Trump’s presidential election victory.Shares of Tesla continued to slide on Friday, in what appeared to be a case of investors taking profits from the electric car maker’s blistering post-U.S. election rally.As of around 6:30 a.m. ET, the firm’s shares were down 5% in U.S. premarket trading, extending losses from earlier in the week. On Wednesday, Tesla shares slumped 8% to post their worst day since before Donald Trump’s presidential election victory in November.Trump’s win prompted a sharp rally in Tesla shares, as investors increased their bets that the electric vehicle firm would benefit thanks to its CEO Elon Musk’s close ties to the president-elect. Musk was appointed by Trump to co-lead the newly created Department of Government Efficiency, also referred to as “DOGE.” The proposed presidential advisory commission’s acronym shares the same name as the internet meme that inspired so-called “memecoin” cryptocurrency, dogecoin.Dogecoin briefly shot up in price after the body’s creation.Musk was a major backer of Trump during the Republican’s election run, pouring in $277 million primarily into his campaign effort, according to Federal Election Commission filings. Musk is the world’s richest person, with a net worth of $439.4 billion, according to Forbes data.Last month, Bloomberg News reported Trump’s transition team was planning to pursue a federal framework for regulating self-driving vehicles.Tesla and Trump’s transition team did not immediately respond to a CNBC request for comment on the report.If true, the move would offer a major boost to Musk’s EV firm. Tesla is staking its future on the idea of rolling out mass fleets of autonomous vehicles, known as “robotaxi” services. At the firm’s “We Robot” event in October, Musk unveiled the firm’s Cybercab self-driving concept car.Tesla has yet to deliver on Musk’s promise of offering truly autonomous vehicles. Tesla’s Autopilot and paid “Full Self-Driving” services still require a human behind the wheel to supervise the system’s actions and take over if needed.In other Tesla-related news, data released by the European Automobile Manufacturers Association on Thursday showed sales of Tesla cars declined 40.9% in November, exceeding the overall 9.5% dip in sales of battery electric cars (BEVs) in the bloc.