The Department of Justice will end up finding itself playing a game of "whack-a-mole," working to compel every third-party encryption vendor within its jurisdiction to build backdoors into its products. Yet even if the government finds a way to win this game it will still lose.
Sooner or later, companies located in countries beyond the U.S. Department of Justice's legal jurisdiction will develop and sell their own encryption tools – companies that the U.S. Department of Justice will be unable to compel to install backdoors.
Meanwhile, the negative impact of creating these backdoors in hardware and software products is significant. Corporations and individuals will no longer trust that the data they save on their smart phones, PCs and other computing devices is safe – unless they add complex and expensive third-party encryption tools to these devices themselves.
Also, computing device manufacturers would likely need to create whole new teams to manage the hundreds to thousands of unlock requests they are likely to get from not just the federal government, but state, local, and foreign governments as well.
Moreover, creating backdoors to access encrypted data on endpoint devices is not a silver bullet that will win the war on terrorism. If law enforcement agencies have a suspect in their sights, there are many tools, processes and capabilities they can leverage to gather data that will further their investigations. Trying to decrypt data on an endpoint, while very valuable, isn't the only option.