Federal law needs to change, this is just showing us how badly this needs to happen. They will fight the hardest right as they realize they could lose, imo. Law Enforcement stands to lose the most from legalization. Everybody else will make $$ or have it better but they will have to go after other folks.
Law enforcement absolutely has the most to loose if Cannabis is made legal. However there are still lots of people out there who would stand to loose a serious amount of money if it is legalized. Think about it this way, most Cannabis growers and breeders are not paying taxes on their product or their business. This is only true because of the legal status of the plant. When it is legalized they will have to pay business taxes and taxes on their product sales, not to mention facilities, employees, and all the other costs that go along with a legitimate business. Think about it this way, if the growers of California really wanted Cannabis legalized it would be sharing the same status as Washington and Colorado. It is not only those who dislike marijuana who vote against the legalization initiatives, it is growers who see their profit margins taking a serious hit who also vote against, or at least don't vote for, Cannabis legalization.
We can also take a look at New York. Upstate NY is not unlike NorCal in that it is still mostly rural areas and many of the areas with urban and suburban populations are economically depressed. However there is still lots of Cannabis being produced in those areas and lots of smokers to buy it all. And then there is New York City, there are so many people in the city alone who smoke, if they all voted it could be legal in that state, but it is not. So why does NY not even have medical marijuana? Because there are lots of people making money off of it as it is and they know legalization will eat into their profits.
None of this takes into account the big businesses that will move in and take out some of our favorite seed producers and a fair amount of those growing commercially. Phillip Morris has been poised since the 90's to capitalize on Cannabis legalization; they have actually prepared themselves to sell Marley brand and Panama Red brand packaged joints.
So while law enforcement would see whole departments and agencies close or dwindled down to an insignificant size, there are lots of people who will loose out if Cannabis is given full legal status in the USA.