What happened After jumping 11% on Wednesday, and almost 38% just since Monday's closing price, shares of Nikola (NASDAQ: NKLA) are giving some of those gains back today. As of 1:55 p.m. EST, shares were down 17.5% on the day. Why the wild three-day ride? Several factors are likely contributing. So what On Monday night, President Joe Biden signed a "Buy America" executive order, and highlighted his support for electric vehicles at the same time. Biden specifically said, "The federal government also owns an enormous fleet of vehicles, which we're going to replace with clean electric vehicles made right here in America, by American workers." Nikola Two and Tre semi trucks. Image source: Nikola. Shares of Nikola and other U.S. electric vehicle makers surged on that comment Tuesday. Yesterday, General Motors (NYSE: GM) announced a hydrogen fuel cell supply agreement with Navistar (NYSE: NAV) for semitrucks. Nikola stock jumped yesterday, and it could have been due to support for hydrogen-fueled semitrucks this agreement implies. Or perhaps it was caught up in the wild short squeeze trading. As of mid-January Nikola had about 35% of its float held short, according to MarketWatch. Today, however, Nikola is giving back those gains. Now what While the GM news may support the relevance of Nikola's plans for hydrogen-fueled semitrucks, it had to be painful for Nikola management. A well-publicized potential agreement between Nikola and GM fizzled in size late last year when Nikola's credibility came into question. The new agreement between GM and Navistar certainly creates a strong and established competitor for Nikola's planned vehicles. Investors today may be questioning if there is enough room for both, assuming the technology even emerges as an efficient alternative to battery-electric vehicles. 10 stocks we like better than Nikola CorporationWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Nikola Corporation wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of November 20, 2020 Howard Smith owns shares of Nikola. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source