Please tell me how to explain to a client who had been charged with 1 count of obtaining money by false pretense the viability of the double jeopardy defense while not focusing on any substantive defense of the crime itself
Unless a great deal has happened in this case that you have not mentioned in your question, there is no way that a defense of double jeopardy will be viable. Such a defense would only be viable if your client had somehow been tried already by the same level of government for the same crime.
The Fifth Amendment to the Constitution of the United States prohibits the government from subjecting a person to “double jeopardy.” In essence, this means that the government can only try a person once for a given crime. This is meant in large part to prevent the government from ruining a person’s life by trying them over and over again even though there was not enough evidence to convict them of the crime. If the government were to do this, the person could run out of money for lawyers, lose their job, and suffer from many other problems. In addition, the government might get “lucky” at some point and the person could be convicted unjustly. The Constitution wanted to guard against this sort of government action.
In the case that you describe, there is no reason to believe that your client is suffering from double jeopardy. In order to claim double jeopardy, the client must have actually been brought to trial (they can’t just be charged with the crime) for this crime. In addition, the trial would have to have ended in a verdict. In other words, it could not have ended in a mistrial or a hung jury. Lastly, the trial would have to have been conducted by the same “sovereign” that is no attempting to try your client. In other words, double jeopardy only applies if the state (as opposed to the state and the federal government) has already tried your client and is now attempting to do so again.
For these reasons, I would suggest that the client should be told that double jeopardy is not a viable defense unless he or she has previously been tried for this crime.