Andrew Lichtenstein/Getty ImagesThe port strike could spark a US recession if it lasts four weeks or longer, Sea-Intelligence's Alan Murphy said.The researcher estimated that the strike will cost the US $3 billion to $5 billion a day.Shipping costs and delays could escalate, impacting global trade if the strike continues.The economy could see a hard landing if the ongoing port strike lasts long enough, according to one industry researcher.Alan Murphy, the CEO of the liner research firm Sea-Intelligence, estimates the US could tip into recession if the port strike lasts longer than a month.