Opinions on cryptocurrencies have been varied in the US. Digital currencies have faced strong opposition from regulators and skeptics who are suspicious of Bitcoin and other alternate currencies. As a result, United States Cryptocurrency regulation is some of the most strict in the world.
Much of this is due to the country's strong stance against money laundering, and the government's efforts to fight the funding of terrorism both domestically and abroad. Many officials see cryptocurrencies as a threat to this mission. While the US does have strict regulations involving exchanges and other websites where you buy and sell these coins, the most strict rules generally are for ICOs, also known as Initial Coin Offerings.
In the Unites States, tokens offered to investors through crowd sale structures are defined as securities. As such, they are subject to many more regulations than traditional coins are. The distinction here is usually made when investors purchased their coins through a crowdfunding event rather than earning them through mining or purchasing them from third parties after the fact on exchanges.
Unfortunately for investors, this often means that they are either excluded from these startup sales when ICO teams do not want to deal with the headaches of including them, or they must go through a rigorous verification procedure in order to participate. Regardless, it is legal to trade digital currencies in the US, and investors should have no problems doing so if they follow proper procedures.