Are cryptocurrencies a threat to the dollar?
Personally, I do not think so?
In general yes,because if most of the countries will allow the cryptocurrencies to be used by the people,it can replace the fiat and banking system which is why cryptocurrencies are created.But it will be too hard for our community to expand in most countries because the super power countries are has some regulations or limit to cryptocurrencies today,like U.S and China these countries has some influence to other small countries.
Even if we speak in general terms about the usage of cryptocurrencies in most countries, it will still not be a threat to USD because it is a decentralized money that our government can't get a control over it. They will just create regulations that will hinder us in gaining the most out o it. Even so, cryptocurrencies can be used side by side without giving a threat to one another, it can just used as an alternative payment for online transactions.