You are asking two questions, one in the title and one in the thread. Addressing the latter first;
Do you think with the level of civilization in the united states, that the digital dollar will be successful?
Yes, it's a possibility. Digital exposure is quite high in the U.S, and having an extra layer on that using the block chain could definitely be successful. It could create a cheaper and faster way to transact using the USD, than what is available today, while giving the government more control of transactions.
Will digital dollar be a threat to bitcoin?
Is the regular dollar a threat to Bitcoin? It isn't, so a digital version, or more specifically a blockchain version would not be any different.
People use Bitcoin for a couple of reasons;
As a global currency,
For privacy,
For freedom,
As an asset and/or hedge fund,
As a speculative asset, etc.
A CBDC would not fill this and attract those users to hold them instead.