The Dow Jones Industrial Average midday Monday was trading near session lows, amid a firming U.S. dollar. Last week, investor sentiment was buffeted by a rapid decline in crude-oil prices CLZ8, +1.16% which fell into bear-market territory, defined as a drop from a recent peak of at least 20%. And while that threat has stabilized somewhat, with the Organization of the Petroleum Exporting Countries considering cuts to production to address rising crude-oil inventories, a new problem appears to be knocking stocks around. Some market participants were attributing a rise in the dollar to a roughly 1 1/2-year high as one of the key factors producing fresh headwinds for the broader market.