Beijing is showing the Trump administration that tariffs aren’t the only weapon in a trade war.

Long before President Donald Trump fired the opening shots of a new U.S.-China trade war from the White House Rose Garden last week, Beijing had been working to perfect its stealth campaign blocking key U.S. agriculture and energy exports. The Chinese government over the past four months has halted or significantly curtailed direct imports of major U.S. commodities including beef, poultry and liquefied natural gas through an array of bureaucratic blocks and tricky third-party sales deals.The so-called nontariff barriers to trade are even stickier than the escalating tariffs rippling across the global economy, analysts said. All together, the moves are an escalation of the curbs China has been honing since its bans on genetically modified foods a decade ago. And they provide Beijing added firepower in the ongoing U.S.-China trade war by targeting exports from Trump-friendly, deep-red states — think Iowa and Nebraska — with restrictions immune to possible workarounds for tariff barriers.