Although Citi called General Dynamics' decision to offer earnings guidance through 2020 in its last earnings report a "welcome" development, the analyst worries that at a share price more than 19 times earnings (General Dynamics stock actually costs 20 times earnings today), all of the good news this company can possibly report is already baked into the stock price. There's simply not much more upside left in the stock, and Citi thinks you should sell it.