Already hit by steel tariffs, investors in pipeline infrastructure are now running for cover. : President Trump's tariffs on imported steel were the first bit of bad news for investors in America's pipeline infrastructure. A worse surprise came today, sending MLP investors into a panic. At midday Energy Transfer Partners is down 8.5%, Williams Companies is off nearly 12%, Enbridge down 7% and Enterprise Products Partners down 6%. The Alerian MLP exchange traded fund has shed 7%.