Construction and engineering company Argan (AGX -4.00%) stumbled on the stock market Tuesday. Following news of an analyst's recommendation downgrade, investors sold out of the stock to leave it with a 4% decline over the trading session. That was a worse performance than that of the bellwether S&P 500 index, which eked out a marginal gain of less than 0.1%.Approaching overvalued territory?The pundit responsible for the downgrade was Lake Street Capital Markets' Rob Brown, who changed his Argan recommendati ...